Crawly Crypt Collection 1/crawlyvol1.bin/program/compiler/vici_102/examples/fib.e

Text File | 1993-01-14 | 985b | 65 lines

class fib
feature
p , f: integer;
create is
do
    io.putstring("Fibbonacci-Berechnung von ");
    io.readint;
    p := io.lastint;
    io.putstring("(I)terativ oder (R)ekursiv berechnen ?");
    io.readchar;
    inspect io.lastchar
    when 'I', 'i' then
        f := fibI(p)
    when 'R', 'r' then
        f := fibR(p);
    else
        f := fib(p); -- who knows what!?
    end;

    -- Ausgabe...
    io.putstring("fib(");
    io.putint(p);
    io.putstring(") = ");
    io.putint(f);
    io.new_line;
end;

fib(p: integer): integer is
require p>=0
do
    result := fibI(p)
end;


fibR(p: integer): integer is
-- Fibbonacci rekursiv berechnen!
do
    if p > 1 then
        result := fibR(p-1) + fibR(p-2)
    else
        result := 1;
    end
end;

fibI(p: integer): integer is
-- Fibbonacci iterativ berechnen!
local f1,f2,n: integer
do
    from f1:=1
    invariant -- Result=fib(n) and (n=0 or (f1=fib(n) and f2=fib(n-1)))
    until n = p
    loop
        Result:=f1+f2;
        f2:=f1;
        f1:=Result;
        n:=n+1;
    end
end

end