Simple C code, "IFs" working, whats wrong?

Asked Mar 29 '16 at 20:01

Active Mar 29 '16 at 20:19

Viewed 63 times

So, here is the code:

#include <stdio.h>

int main (int argc, char **argv)
{
    float num;

    printf ("Choose one: 1.2 or 2.4 or 3.6 or 4.8: ");
    scanf ("%3f",&num);
    printf("\nTEST = %f\n",num);

    if (num == 1.2)
        printf("\n you selected the first (1.2)\n");

    if (num == 2.4)
        printf("\n you selected the secon (2.4)\n");

    if (num == 3.6)
        printf("\n you selected the third (3.6)\n");

    if (num == 4.8)
        printf("\n you selected the fourth (4.8)\n");

    return 0;
}

It's just a simple assignment, I can use only if, can't use else, but the code simply refuses to work. I wrote it with Gedit and compiled with GCC (ubuntu). Already tested with CodeBlocks, Dev-C++ (Windows 8) and CppDroid (Android). The problem is that none of the IFs seem to work and show the 'printf', what am I doing wrong?

edited Mar 29 '16 at 20:19

John Odom

1,189
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asked Mar 29 '16 at 20:01

Gustavo MN - Sbrobol

4

Rounding/representation errors. Don't use exact comparison on floating point. Check for an acceptable range instead. – too honest for this site Mar 29 '16 at 20:03
Workaround: Read strings, not floats... – Karoly Horvath Mar 29 '16 at 20:07
Never test floating point for equality. – Weather Vane Mar 29 '16 at 20:09
how can i test it? – Gustavo MN - Sbrobol Mar 29 '16 at 20:11
FYI, assuming your libc supports it, you can get the exact value of a floating point number by using printf's `%a` conversion specifier. Try adding `printf("%a\n%a\n", num, 1.2)` after your `scanf` statement, enter `1.2` at the prompt, and see what happens. – Tim Mar 29 '16 at 20:11
Don't even test it. Give your menu 4 options. – Weather Vane Mar 29 '16 at 20:12
You must add an 'F' or 'f' after the floating point literals, i.e. 1.2f, in order for the compiler to know that the value is a float and not a double type. 1.2 in double type is not the same as 1.2 stored in num which is a float type. – Dan Randolph Mar 29 '16 at 20:19
Thanks @DanRandolph using the 'F' after the numbers worked. :) – Gustavo MN - Sbrobol Mar 29 '16 at 20:32
Also thanks everyone for all the useful information. – Gustavo MN - Sbrobol Mar 29 '16 at 20:35
"marked as duplicate by Idos, Olaf, jpw, juanchopanza c Mar 29 at 20:09 This question was marked as an exact duplicate of an existing question." The referenced answer is a long way from being the answer to this question, as anyone who actually knows anything about IEEE floating point processing used in the C language. – Dan Randolph Apr 04 '16 at 18:02

Simple C code, "IFs" working, whats wrong?

0 Answers0