Question

I am using DevC++ 4.9, running on WinXP SP3 (32bit), here is the code:

#include <stdio.h>
#include <stdlib.h>

main(int argc, char *argv[])
{
    double value;

    int i;

    printf("Enter double: ");
    scanf("%lf", &value);
    i = value*100;
    printf("double: %lf\n", value);
    printf("int: %d\n", i);

  system("PAUSE");  
}

I have entered different values and here are the results:

Test 1:

Test 2:

Test 3:

Why Test 1 and Test 2 displayed different results??

Answer 1

This is due to floating-point round-off:

What Every Computer Scientist Should Know About Floating-Point Arithmetic:
http://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html

3.07 cannot be exactly represented in binary. In your case, it’s being rounded to slightly less than 3.07, therefore 100 * 3.07 is evaluating to 306.9999999..., which is truncated to 306.

Same applies to 3.05. But 3.06, is rounded slightly up. So 100 * 3.06 correctly shows up as 306.