atof()                  Convert String to Double

 #include   <math.h>
 #include   <stdlib.h>                   Use either math.h or stdlib.h

 double     atof(string);                Value of converted string
 const char *string;                     String to be converted

    atof() converts 'string' to a double-precision, floating-point value.
    'string' is a sequence of characters that can be interpreted as a
    numeric value; it has the following format:

     [whitespace][sign][digits][.digits][{e|E}[sign]digits]

     where:
        whitespace  any number of tab and space characters are ignored
        sign        + or -
        digits      one or more decimal digits
        e|E              exponent prefixes

    A decimal point must be followed by a digit; if there are no digits
    before the decimal point, then at least one digit must appear after
    it. atof() stops reading input at the first character it cannot
    recognize as part of the number (likely the null character
    terminating the string).

       Returns:     The double value of 'string'.  If 'string' cannot be
                    converted to a double value, then 0.0 is returned.
                    The return value is undefined for overflow; 0.0 is
                    returned on underflow.

   -------------------------------- Example ---------------------------------

    The following statements convert several strings to double values and
    print the values.

           #include <math.h>
           #include <stdio.h>

           main()
           {
               double x, y, z;

               x = atof("    -.625e-3  (this will be -0.000625)");
               y = atof("0");
               z = atof("  143248291283472348923874.2134762734E222\n");
             /* prints: x=-6.250000e-004, y=0.000000e+000, z=1.432483e+245 */
               printf("x=%e, y=%e, z=%e\n", x, y, z);
           }