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CEnvi Shareware Manual, Chapter 2:
Cmm Language Tutorial
CEnvi unregistered version 1.009
29 November 1994
CEnvi Shareware User's Manual
Copyright 1993, Nombas, All Rights Reserved.
Published by Nombas, PO BOX 875, MEDFORD MA 02155-0007 USA
(617)391-6595
Thank you for trying this shareware version of CEnvi from Nombas,
a member of the Association of Shareware Professionals (ASP).
2. The Cmm Language: Tutorial for Non-C Programmers
The information in this chapter is geared toward those who are
not familiar with the C programming language. C programmers
should jump ahead to the next chapter: Cmm versus C. This
section is an introduction to and description of the Cmm
programming language.
If you can write a batch, script, or macro file, or if you can
remember what "y = x + 1" means from your algebra class, then
you're ready to take on Cmm. Really. Cmm contains only
variables, mathematics symbols (remember algebra), and these few
statements: IF, ELSE, DO, WHILE, FOR, SWITCH, CASE, BREAK,
DEFAULT, CONTINUE, GOTO, and RETURN.
This section is an abbreviation of the Cmm Language Tutorial
chapter in the CEnvi registered manual. The CEnvi registered
manual goes into much more depth, has many more examples, and
follows a step-by-step tutorial to create a simple text editor
with CEnvi.
2.1. Your first Cmm program
Before going into a description of Cmm, let's first make sure
that CEnvi is working properly. With a text editor (e.g., EDIT
for DOS, E for OS/2, or NOTEPAD for Windows) create the file
HELLO.CMM and enter this text:
// Hello.cmm: My first Cmm program
Count = 1; /* Count is how many Cmm programs I've written */
printf("Hello world. This is my %dst Cmm program.\n",Count);
printf("Press any key to quit...");
getch();
You have now written a Cmm program named "HELLO.CMM". Don't be
concerned if you do not yet understand the HELLO.CMM program; it
should become clear as Cmm is defined. Now execute this program
(for DOS or OS/2 you would enter "CENVI HELLO.CMM" and for
Windows you need may use the File Manager and double-click on the
file name). You should get this output:
Hello world. This is my 1st Cmm program.
Press any key to quit...
If this program will execute, then you are ready to go on to
learn about Cmm. If it did not execute then consult the CEnvi
installation section in the first chapter of this shareware
manual.
2.2. Cmm comments
Comments are used in Cmm code to explain what the code does, but
the comment itself does nothing. Comments are very useful in
programming. A comment takes nothing away from the execution of
a program, but adds immeasurably to the readability of the source
code.
In Cmm, any text on a line following two slash characters (//) is
considered a comment and so is ignored by the Cmm interpreter.
Likewise, anything between a slash-asterisk (/*) and an
asterisk-slash (*/) is a comment (this type of comment may extend
over many lines). In the HELLO.CMM program there is a "//"
comment on the first line and a "/* blah blah */" comment on the
second line.
2.3. Cmm primary data types
There are three principal data types in Cmm:
*Byte: A character (e.g., 'D') or a whole number between 0 and
255, inclusive
*Integer: A whole number value; this is the most common numeric
data type (examples: 0, -1000, 567, 4335600)
*Float: floating point numbers; any number containing a decimal
point (examples: 0.567, 3.14159, -5.456e-12)
Cmm determines the data type of a number by how it is used; for
example, in the HELLO.CMM program the "1" in the second line is
an integer because that is the default type for numbers without a
decimal point.
2.3.1 Escape Sequences for Characters
Certain characters are represented with a multi-character
sequence beginning with a backslash (\). These are called escape
sequences, and have the following meanings:
\a Audible bell
\b Backspace
\f Formfeed
\n Newline
\r Carriage return
\t Tab
\v Vertical tab
\' Single quote
\" Double quote
\\ Backslash character
\### Octal number // ex: '\033' is escape character
// ex: \0 is null character
\x## Hex number // '\x1B' is escape character
2.4. Cmm Variables
A Cmm variable is a symbol that may be assigned data. The
assignment of data is usually performed by the equal sign (=), as
in the line "Count = 1" in HELLO.CMM. After variables have been
assigned, they can be treated as their data type. So, after
these statements:
Count = 1 // assign count as the integer 1
Count = Count + 2 // same as: Count = 1 + 2
Count would now have the value 3.
2.5. Cmm Expressions, Statements, and Blocks
A Cmm "expression" or "statement" is any sequence of code that
perform a computation or take an action (e.g., "Count=1",
"(2+4)*3"). Cmm code is executed one statement at a time in the
order it is read. A Cmm program is a series of statements
executed sequentially, one at a time. Each line of HELLO.CMM,
for example, follows the previous line as it is written and as it
is executed.
A statement usually ends in a semicolon (;) (this is required in
C, and still a good idea in Cmm to improve readability). Each
program statement is usually written on a separate line to make
the code easy to read.
Expressions may be grouped to effect the sequence of processing;
expressions inside parentheses are processed first. Notice that:
4 * 7 - 5 * 3 // 28 - 15 = 13
has the same meaning, due to algebraic operator precedence, as:
(4 * 7) - (5 * 3) // 28 - 15 = 13
but has a different meaning than:
4 * (7 - 5) * 3 // 4 * 2 * 3 = 8 * 3 = 24
which is still different from:
4 * (7 - (5 * 3)) // 4 * (7 - 15) = 4 * -8 = -32
A "block" is a group of statements enclosed in curly braces ({})
to show that they are all a group and so are treated as one
statement. For example, HELLO.CMM may be rewritten as:
// Hello.cmm: My first Cmm program
Count = 1; /* Count is how many Cmm programs I've written */
printf("Hello world. This is my %dst Cmm program.\n",Count);
{
// this block tells the user we're done, and quits
printf("Press any key to quit...");
getch();
}
The indentation of statements is not necessary, but is useful for
readability.
2.6. Cmm Mathematical Operators
Cmm code usually contains some mathematical operations, such as
adding numbers together, multiplying, dividing, etc. These are
written in a natural way, such as "2 + 3" when you want to add
two and three. The next few subsections define the recognized
operators within the comments of sample code:
2.6.1 Basic Arithmetic
// "=" assignment: sets a variable's value
i = 2; // i is 2
// "+" addition: adds two numbers
i = i + 3; // i is now (2+3) or 5
// "-" subtraction: subtracts a number
i = i - 3; // i is now (5-3) or 2 again
// "*" multiplication:
i = i * 5; // i is now (2*5) or 10
// "/" division:
i = i / 3; // i is now (10/3) or 3 (no remainder)
// "%" remainder: remainder after division
i = 10;
i = i % 3; // i is now (10%3) or 1
2.6.2 Assignment Arithmetic
Each of the above operators can combined with the assignment
operator (=) as a shortcut. This automatically assumes that the
assigned variable is the first variable in the arithmetic
operation. Using assignment arithmetic operators, the above code
could be simplified as follows:
// "=" assignment: sets a variable's value
i = 2; // i is 2
// "+=" assign addition: adds number
i += 3; // i is now (2+3) or 5
// "-=" assign subtraction: subtracts a number
i -= 3; // i is now (5-3) or 2 again
// "*=" assign multiplication:
i *= 5; // i is now (2*5) or 10
// "/=" assign divide:
i /= 3; // i is now (10/3) or 3 (no remainder)
// "%=" assign remainder: remainder after division
i = 10;
i %= i % 3; // i is now (10%3) or 1
2.6.3 Auto-Increment (++) and Auto-Decrement (--)
Other arithmetic shortcuts are the auto-increment (++) and
auto-decrement (--) operators. These operators add or subtract 1
(one) from the value to which they are applied. ("i++" is a
shortcut for "i+=1", which is itself shortcut for "i=i+1").
These operators can be used before (prefix) or after (postfix)
their variables. If used before, then the variable is altered
before it is used in the statement; if used after, then the
variable is altered after it is used in the statement. This is
demonstrated by the following code sequence:
i = 4; // i is initialized to 4
j = ++i; // j is 5, i is 5 (i was incremented before use)
j = i++; // j is 5, i is 6 (i was incremented after use)
j = --i; // j is 5, i is 5 (i was decremented before use)
j = i--; // j is 5, i is 4 (i was decremented after use)
2.7. Cmm Arrays and Strings
An "array" is a group of individual data elements. Each
individual item in the array is then called an "array element".
An element of an array is itself a variable, much like any other
variable. Any particular element of the array is selected by
specifying the element's offset in the array. This offset is an
integer in square brackets ([]). For example:
prime[0] = 2;
prime[1] = 3;
prime[2] = 5;
month[0] = "January";
month[1] = "February";
month[2] = "March";
An array in Cmm does not need to be pre-defined for size or data
type, as it does in other languages. Any array extends from
minus infinity to plus infinity (within reasonable computer
memory limits). The data type for the array is the type of the
data first assigned to it.
If Cmm code begins with:
foo[5] = 7;
foo[2] = -100;
foo[-5] = 4;
then foo is an array of integers and the element at index 7 is a
5, at index 2 is -100, and at index -5 is 4. "foo[5]" can be
used in the code anywhere that a variable could be used.
2.7.1 Array Initialization
Arrays can be initialized by initializing specific elements, as
in:
foo[5] = 7; foo[2] = -100; foo[-5] = 4;
or by enclosing all the initial statements in curly braces, which
will cause the array to start initializing at element 0, as in:
foo = { 0, 0, -100, 0, 0, 7 };
2.7.2 Strings
Strings are arrays of bytes that end in the null-byte (zero).
"String" is just a shorthand way to specify this array of bytes.
A string is most commonly specified simply by writing text within
two quote characters (e.g., "I am a string.")
If this statement were present in the Cmm code:
animal = "dog";
it would be identical to this statement:
animal = { 'd', 'o', 'g', 0 };
and in both cases the value at animal[0] is 'd', at animal[2] is
'g', and at animal[3] is 0.
Escape sequences encountered in strings will be translated into
their byte value. So you'll often see strings such as "\aHello
world\n" where the "\a" means to beep and the "\n" means to put a
newline character at the end of the string. Cmm provides the
back-quote (`), also known as known as the "back-tick" or "grave
accent", as an alternative quote character to indicate that
escape sequences are not to be translated. So, for example, here
are two ways to describe the same file name:
"c:\\autoexec.bat" // traditional method
`c:\autoexec.bat` // alternative method
2.7.3 Array Arithmetic
When one array is assigned to the other, as in:
foo = "cat";
goo = foo;
then both variables define the same array and start at the same
offset 0. In this case, if foo[2] is changed then you will find
that goo[2] has also been changed.
Integer addition and subtraction can also be performed on arrays.
Array addition or subtraction sets where the array is based. By
altering the previous code segment to:
foo = "cat";
goo = foo + 1;
goo and foo would now be arrays containing the same data, except
that now goo is based one element further, and foo[2] is now the
same data as goo[1].
To demonstrate:
foo = "cat"; // foo[0] is 'c', foo[1] = 'a'
goo = foo + 1;// goo[0] is 'a', goo[-1] = 'c'
goo[0] = 'u'; // goo[0] is 'u', foo[1] = 'u', foo is "cut"
goo++; // goo[0] is 't', goo[-2] = 'c'
goo[-2] = 'b' // goo[0] is 't', foo[0] = 'b', foo is "but"
2.7.4 Multi-Dimensional Arrays: Arrays of Arrays
An array element is a variable, and so if the type of that
element's variable is itself an array, then you have an array of
arrays. A statement such as:
goo[4][2] = 5;
indicates that goo is an array of arrays, and that element 2 of
element 4 is the integer 5.
Multi-dimensional arrays might be useful for programming a
tic-tac-toe game. Each row and column of the 3x3 board could be
represented with a row, column element containing 'X', 'O' or ' '
(blank) depending on the character at that location. For
example, a horizontal 'X' win in the middle row could be
initialized like this:
board[1][0] = 'X';
board[1][1] = 'X';
board[1][2] = 'X';
Note that a string is an array, and so anytime you make an array
of strings you are defining an array of arrays.
2.8. Cmm Structures
A "structure" is a collection of named variables that belong
together as a whole. Each of the named variables in a structure
is called a member of that structure and can be any data type
(integer, float, array, another structure, array of structures,
etc.). These structure members are associated with the structure
by using a period between the structure variable and the member
name.
A simple and useful example of a structure is to specify a point
on the screen. A point is made up of a row and column, and so
you may specify:
place.row = 12; // set to row 12
place.col = 20; // set at column 20
place.row--; // move up one row to row 11
Two structures can be compared for equality or inequality, and
they may be assigned, but no other arithmetic operations can be
performed on a structure.
2.9. printf() and getch()
Although although the Cmm "function" has not yet been defined, it
is useful to use two functions already, printf() and getch(), for
learning more about Cmm programming. Unfortunately, printf() is
about as complicated as a function can get.
2.9.1 printf() Syntax
printf() prints to the screen, providing useful feedback on your
programming. The basic syntax of printf() is this:
printf(FormatString,data1,data2,data3,...);
FormatString is the string that will be printed to the screen.
When FormatString contains a percent character (%) followed by
another character, then instead of printing those characters
printf() will print the next data item (data1, data2, data3,
etc...). The way the data will be presented is determined by the
characters immediately following the percent sign (%). There are
many such data formats, as described fully in the Registered
User's Manual (or any C programming manual), but here's few to
start with:
*%% print a percentage sign
*%d print a decimal integer
*%X print a hexadecimal integer
*%c print a character
*%f print a floating-point value
*%E print a floating-point value in scientific format
*%s print a string
There are also special characters that cause unique screen
behavior when they are printed, some of which are:
*\n goto beginning of next line
*\t tab
*\a alarm: audible beep
*\r carriage-return without a line feed
*\" print the quote character
*\\ print a backslash
Here are some example printf() statements:
printf("Hello world. This is my %dst Cmm program.\n",Count);
printf("%c %d %dlips",'I',8,2);
printf("%d decimal is the same as %X in hexadecimal",n,n);
printf("My name is: %s\n","Mary");
2.9.2 getch() Syntax
getch() (GET CHaracter) waits for any key to be pressed. The
program stops executing at the getch() statement until a key is
pressed. getch() is especially useful in Windows because once a
program is completed its windows will go away. So getch() might
be placed at the end of the program to keep the screen visible
until a key is pressed.
2.9.3 Using printf() and getch() to Learn Cmm
You can now experiment with what you are learning by using the
printf() and getch() statements.
If, during program execution, you want to know that you're about
to execute an exciting piece of code, then before those
interesting lines of code you may want to write:
printf("Here comes the good stuff. Press any key...");
getch();
You can display values at any point in your program with a
printf() statement. This short TEST.CMM program tests how "*="
works:
// TEST.CMM - test the *= operator
var1 = 4;
var2 = 5;
printf("the numbers are %d and %d\n",var1,var2);
var1 *= 7;
var2 *= 7;
printf("after *= 7 the values are %d and %d\n",var1,var2);
getch();
2.10. Bit Operators
Cmm contains many operators for operating on the binary bits in a
byte or an integer. If you're not familiar with hexadecimal
numbering (digits '0' to 'F'), you may want to refer to the CEnvi
Registered User's Manual.
i = 0x146;
// "<<" shift left: shift all bits left by value
// "<<=" assignment shift left
i <<= 2; // shift i (0x146) left 2, so i = 0x518
// ">>" shift right: shift all bits right by value
// ">>=" assignment shift right
i >>= 3; // shift i (0x518) right 3, so i = 0xA3
// "&" bitwise AND
// "&=" assignment bitwise and
i &= 0x35; // and i (0xA3) with 0x35 so i = 0x21
// "|" bitwise OR
// "|=" assignment bitwise OR
i |= 0xC5; // OR i (0x21) with 0xC4 so i = 0xE5
// "^" bitwise XOR: exlusive OR
// "^=" assignment bitwise XOR
i ^= 0xF329 // XOR i (0xE5) with so i = 0xF3CC
// "~" Bitwise complement: (turn 0 bits to 1, and 1 to 0)
i = ~i; // complement i (0xF3CC) so i = 0xFFFF0C33 (OS/2)
2.11. Logical Operators and Conditional Expressions
A conditional expression is evaluated to be TRUE or FALSE, where
FALSE means zero, and TRUE means anything that is not FALSE
(i.e., not zero). A variable or any other expression by itself
can be TRUE or FALSE (i.e., non-zero or zero). With logic
operators, these expressions can be combined to make encompassing
TRUE/FALSE decisions. The logic operators are:
* "!" NOT: opposite of decision
!TRUE // FALSE
!FALSE // TRUE
!('D') // FALSE
!(5-5) // TRUE
* "&&" AND: TRUE if and only if both expressions are true
TRUE && FALSE // FALSE
TRUE && TRUE // TRUE
0 && (foo+2) // FALSE: (foo+2) is not evaluated
!(5-5) && 4 // TRUE
* "||" OR: TRUE if either expression is TRUE
TRUE || FALSE // TRUE: doesn't even check FALSE
TRUE || (4+2) // TRUE: (4+2) is not evaluated
FALSE || (4+2) // TRUE: (4+2) is evaluated
FALSE || FALSE // FALSE
0 || 0.345 // TRUE
!(5-3) || 4 // TRUE
* "==" EQUALITY: TRUE if both values equal, else FALSE
5 == 5 // TRUE
5 == 6 // FALSE
* "!=" INEQUALITY: TRUE if both values not equal, else FALSE
5 != 5 // FALSE
5 != 6 // TRUE
* "<" LESS THAN
5 < 5 // FALSE
5 < 6 // TRUE
* ">" GREATER THAN
5 > 5 // FALSE
5 > 6 // FALSE
5 > -1 // TRUE
* "<=" LESS THAN OR EQUAL TO
5 <= 5 // TRUE
5 <= 6 // TRUE
5 <= -1 // FALSE
* ">=" GREATER THAN OR EQUAL TO
5 >= 5 // TRUE
5 >= 6 // FALSE
5 >= -1 // TRUE
2.12. Flow Decisions: Loops, Conditions, and Switches
This section describes how Cmm statements can control the flow of
your program. You'll notice code sections are often indented,
when blocks belong together; this makes the code much easier to
read.
2.12.1 IF - Execute statement (or block) if conditional expression is TRUE
if ( goo < 10 ) {
printf("goo is smaller than 10\n");
}
2.12.2 ELSE - Execute statement (or block) if IF block was not executed
if ( goo < 10 ) {
printf("goo is smaller than 10\n");
} else {
printf("goo is not smaller than 10\n");
}
ELSE can also be combined with IF to find one in a series of
values:
if ( goo < 10 ) {
printf("goo is less than 10\n");
if ( goo < 0 ) {
printf("goo is negative; of course it's less than 10\n");
}
} else if ( goo > 10 ) {
printf("goo is greater than 10\n");
} else {
printf("goo is 10\n");
}
2.12.3 WHILE - Execute block while conditional expression is TRUE
str = "WHO ARE YOU?";
while ( str[0] != 'A' ) {
printf("%s\n",str);
str++;
}
printf("%s\n",str);
The output of the above code would be:
WHO ARE YOU?
HO ARE YOU?
O ARE YOU?
ARE YOU?
ARE YOU?
2.12.4 DO ... WHILE - Execute block, and then test for conditional
This is different from the WHILE statement in that the block is
executed at least once, before the condition is tested.
do {
value++;
printf("value = %d\n",value);
} while( value < 100 );
The code used to demonstrate the WHILE statement might be better
written this way to avoid the extra printf():
str = "WHO ARE YOU?";
do {
printf("%s\n",str);
} while ( str++[0] != 'A' );
2.12.5 FOR - initialize, test conditional, then loop
"for" is a combination of statements of this format:
for ( initialization; conditional; loop_expression )
statement
The initialization is performed first. Then the conditional is
tested. If the conditional is TRUE (or if there is no
conditional expression) then statement is executed, and then the
loop_expression is executed, and so on back to testing the
conditional. If the conditional is FALSE then the program
continues beyond statement. The "for" statement is a shortcut
for this form of WHILE:
initialization;
while ( conditional ) {
statement;
loop_expression;
}
The above code demonstrating the WHILE statement would be
rewritten this way if you preferred to use the FOR statement:
for ( str = "WHO ARE YOU?"; str[0] != 'A'; str++ )
printf("%s\n",str);
printf("%s\n",str);
2.12.6 BREAK and CONTINUE
"break" terminates the nearest loop or case statement.
"continue" jumps to the test condition in the nearest DO or WHILE
loop, and jumps to the loop_expression in the nearest FOR loop.
2.12.7 SWITCH, CASE, and DEFAULT
The SWITCH statement follows this format:
switch( switch_expression ) {
case exp1: statement1
case exp2: statement2
case exp3: statement3
case exp4: statement4
case exp5: statement5
.
.
.
default: default_statement
}
switch_expression is evaluated, and then it is compared to all of
the case expressions (expr1, expr2, expr3, etc...) until a match
is found (i.e., switch_expression == expr? ). The statements
following that match are then executed until the end of the
switch block is reached or until a BREAK statement exits the
switch block. If no match is found, the DEFAULT: statement is
executed if there is one.
For example, this code handles the variable "key", which is
assumed to be the value of a key that was just pressed on the
keyboard:
switch ( key ) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9:
printf("A digit was pressed\n");
break;
case '\r';
printf("You pressed RETURN\n");
default:
printf("I am not prepared for the key you pressed\n");
break;
}
2.12.8 GOTO and Labels
You may jump to any location within a function block (see
functions) by using the GOTO statement. The syntax is:
goto LABEL;
where LABEL is an identifier followed by a colon (:).
if ( a < 0 ) {
BadGoingsOn: // this is a label
printf("\aThe value for a is very bad.\n");
abort(); // see function library for abort()
} else if ( 1000 < a )
goto BadGoingsOn;
GOTOs should be used sparingly, for they often make it difficult
to track program flow.
2.13. Conditional Operator ?:
The conditional operator is a strange-looking statement that is
simply a useful shortcut. The syntax is this:
test_expression ? expression_if_true : expression_if_false
First, test_expression is evaluated. If test_expression is
non-zero (TRUE) then expression_if_true is evaluated and the
value of the entire expression replaced by the value of
expression_if_true. If test_expression is FALSE, then
expression_if_false is evaluated and the value of the entire
expression is that of expression_if_false.
For example:
foo = ( 5 < 6 ) ? 100 : 200; // foo is set to 100
printf("User's name is %s\n",NULL==name ? "unknown" : name);
2.14. Functions
Functions in Cmm can perform any action of any complexity, and
yet they are used in statements as easily as variables. It is
because of the flexibility and simplicity of functions that Cmm
needs so few statements. Any action can take place in a
function, and yet the function is treated by the calling code
simply as the data type that the function returns.
2.14.1 Function definition
A function takes a form such as this:
FunctionName(Parameter1,Parameter2,Parameter3)
{
statements...
return result;
}
where the function name is followed by a list of input parameters
in parentheses (there can be any number of input parameters and
they can be named with any variable names).
A call is made to a function in this format:
FunctionName(Value1,Value2,Value3)
So any call to FunctionName will be result in the execution of
FunctionName() with the parameters passed, and then be equivalent
to whatever value FunctionName() returns.
2.14.2 Function RETURN Statement
The return statement causes a function to return to the code that
initially called the function. The calling code will receive the
value that the function returned. Here are function examples:
foo(a,b) // return a times b
{
return( a * b );
}
foo(a,b) // return a times b
{
return a * b;
}
foo(a,b) // return the minimum value of a and b
{
if ( a < b )
result = a;
else
result = b;
return(result);
}
foo(a,b) // return a structure with members .min and .max
{ // for the smaller and larger of a and b
if ( a < b ) {
bounds.min = a;
bounds.max = b;
} else {
bounds.min = b;
bounds.max = a;
}
return( bounds );
}
If no value is returned, or if the end of the function block is
reached without a return statement, then no value is returned and
the function is a "void" type. void functions return no value to
the calling code. These examples demonstrate some void-returning
functions:
foo(a,b) // set a = b squared. No return value.
{
a = b * b;
return;
}
foo(a,b) // set a = b squared. No return value.
{
a = b * b;
}
2.14.3 Function Example
The use of functions should gain clarity with this example. This
code demonstrates a function that multiplies two integers
(although multiplying integers could more easily be performed
with the multiply (*) operator):
num1 = 4;
num2 = 6;
// use the standard method of multiplying numbers
printf("%d times %d is %d\n",num1,num2,num1*num2);
// now call our function to do the same thing
printf("%d times %d is %d\n",num1,num2,Multiply(num1,num2));
// declare a function that multiplies two integers. Notice
// that the integers are defined as i and j, so that's how
// they'll be called in this function, no matter what they
// were named in the calling code. This function will
// return i added to itself j times.
Multiply(i,j)
{
total = 0;
for ( count = 0; count < j; count++ )
total += i;
return(total); // caller will receive this value
}
When executed, the above code will print:
4 times 6 is 24
4 times 6 is 24
This example demonstrated several features of Cmm functions.
Notice that in calling printf() the parameter "num1*num2" is not
passed to printf, but the result of "num1*num2" is passed to
printf. Likewise, "Multiply(num1,num2)" is not a parameter to
printf(); instead, printf receives the return value of Multiply()
as its parameter.
2.14.4 Function Recursion
When a function calls itself, or calls some other function that
calls itself, then it is known as a recursive function.
Recursion is permitted in Cmm, as it is in C. Each call into a
function is independent of any other call to that function (see
section on variable scope).
The following function, factor(), factors a number. Factoring is
a natural candidate for recursion because it is a repetitive
process where the result of one factor is then itself factored
according to the same rules.
factor(i) // recursive function to print all factors of i,
{ // and return the number of factors in i
if ( 2 <= i ) {
for ( test = 2; test <= i; test++ ) {
if ( 0 == (i % test) ) {
// found a factor, so print this factor then call
// factor() recursively to find the next factor
printf(" %d",test);
return( 1 + factor(i/test) );
}
}
}
// if this point was reached, then factor not found
return( 0 );
}
2.15. Variable Scope
A variable in Cmm is either global or local. A global variable
is one that is referenced outside of any function, making it
visible and accessible to all functions. A local variable is one
that is only referenced inside of a function, and so it only has
meaning and value within the function that declares it. Note
that two identically-named local variables in different functions
are not the same variable. Also, each instance of a recursive
function has its own set of local variables. In other words, a
variable that is not referenced outside of a function only has
meaning (and that meaning is unique) while the code for that
function is executing.
In the following sample code, "number" is the only global
variable, the two "result" variables in Quadruple() and Double()
are completely independent, and the "result" variable in one call
Double() is unique to each call to Double():
number = Quadruple(3);
Quadruple(i)
{
result = Double(Double(i));
return(result);
}
Double(j)
{
result = j + j;
return(result);
}
Note that variables that are all in uppercase letter are
considered global and refer to environment variables. See the
chapter on CEnvi specifics for more on environment variables.
2.16. #define
"#define" is used to replace a token (a variable or a function
name) with other characters. The structure is:
#define token replacement
This results in all subsequent occurrences of "token" to be
replaced with "replacement". For example:
#define HI "Hello world!"
printf(HI);
would result in the following output:
Hello world!
because HI was replaced with "Hello world!"
A common use of #define is to define constant numeric or string
values that might possibly change, so that in the future only the
#define at the top of the file needs to be altered. For
instance, if you write screen routines for a 25-line monitor, and
then later decide to make it a 50-line monitor, you're better off
altering
#define ROW_COUNT 25
to
#define ROW_COUNT 50
and using ROW_COUNT in your code (or ROW_COUNT-1, ROW_COUNT+2,
ROW_COUNT/2, etc...) than if you had to search for every instance
of the numbers 25, 24, 26, etc...
CEnvi has a large default list of tokens that have already been
#define'd, such as TRUE, FALSE, and NULL. More of these are
listed in the chapter on the Internal Function Library.
2.17. #include
Cmm code is executed from one stream of source code. Sometimes
it is useful to break the program into different files or to
access commonly used code without recreating that code again and
again in every new program written. This is what "#include" is
for: it allows code from another file to be included in a
program.
The #include syntax is:
#include <Name[,Ext[,Prefix[,BeginCode[,EndCode]]]]>
where:
Name - Name of the file to include
Ext - Extension name to add to Name if not already there
Prefix - Will only include code from Name on lines that begin
with this string
BeginCode - Will start including code from Name following
this line of text
EndCode - Will stop including code when this line is read
The quote characters (' or ") may be used in place of < and >.
The only field that is required by Cmm is Name (this is the field
used in C's #include), which is the name of the file to include.
All other fields are optional, and can be left blank if unused.
To include all of C:\CMM\LIB.cmm
#include <c:\CMM\LIB.cmm>
To include from dog.bat between the lines GOTO END and :END
#include 'dog,bat,,GOTO END,:END'
To include lots of little files into one big one program
#include <screen.cmm>
#include <keyboard.cmm>
#include <init.cmm>
#include <comm.cmm>
In CEnvi a file will not be included more than once, and so if it
has already been included, a second (or third) #include statement
will have no effect.
2.18. Initialization
All code that is outside of any function is part of the global
initialization function. This code is executed first, before
calling any function (unless a function is called from this
initialization code).
Any variables referenced in the initialization section are
global.
2.19. main(ArgCount,ArgStrings)
After the initialization has been performed, the main() function
is called and is given the argument input to the Cmm program.
The first parameter to main (ArgCount) is the number of arguments
provided to the program. ArgStrings is an array of those input
arguments, which are always strings. The first argument is
always the name of the source code, or of CEnvi.exe if there is
no source file.
The value returned from main() should be an integer, and is the
exit code (ERRORLEVEL for DOS) returned to the operating system
from your program (see also exit() in the internal library).
This code file TEST.CMM:
printf("I am initializing\n");
main(argc,argv)
{
printf("This program is called %s.\n",argv[0]);
printf("There are %d input arguments, as follows:\n",argc);
for ( i = 0; i < argc; i++ )
printf("\t%s\n",argv[i]);
return(0);
}
printf("still initializing\n");
When executed in this way:
cenvi test.cmm I am 4 "years old" today
would result in this output:
I am initializing
still initializing
This program is called test.CMM.
There are 6 input arguments, as follows:
test.CMM
I
am
4
years old
today
and would return 0 to the operating system.
