Your challenge for this month’s Exercise is to write a sign() function, which returns 1, 0, or -1 depending on the sign of an integer. A relatively simple thing to code — I hope!

For my solution, the sign() function uses two comparisons. Assuming a is the value passed:

if( a<0 ) return(-1);

If a is less than zero, -1 is returned. Otherwise:

if( a>0 ) return(1);

When a is greater than zero, 1 is returned.

The only option left is zero, which is handled by a single return statement:

return(0);

Here is the full code:

2021_03-Exercise.c

#include <stdio.h>

int sign(int a)
{
    /* value is negative */
    if( a<0 ) return(-1);

    /* value is positive */
    if( a>0 ) return(1);

    /* value is zero */
    return(0);
}

int main()
{
    int values[20] = { -34, 27, 0, 48, -25, 28, -55,
        66, -17, -78, 0, -20, 40, -98, 63, -44, 59,
        6, 65, 90
    };
    int x;

    for( x=0; x<20; x++ )
    {
        printf("Sign of %3d is ", values[x] );
        switch( sign( values[x] ))
        {
            case -1:
                puts("negative");
                break;
            case 1:
                puts("positive");
                break;
            case 0:
                puts("zero");
                break;
            default:
                puts("unknown");
        }
    }

    return(0);
}

The output reflects the value returned by the sign() function; text is appended to the value reflecting the proper sign: negative, positive, or zero:

Sign of -34 is negative
Sign of  27 is positive
Sign of   0 is zero
Sign of  48 is positive
Sign of -25 is negative
Sign of  28 is positive
Sign of -55 is negative
Sign of  66 is positive
Sign of -17 is negative
Sign of -78 is negative
Sign of   0 is zero
Sign of -20 is negative
Sign of  40 is positive
Sign of -98 is negative
Sign of  63 is positive
Sign of -44 is negative
Sign of  59 is positive
Sign of   6 is positive
Sign of  65 is positive
Sign of  90 is positive

I hope you found the solution easy and enjoyed the challenge. Remember, my solution represents only one approach; as long as your sign() function behaves similarly, it’s good.

A sign() function comes in handy, which is probably why the BASIC language featured the SGN command that performs the same feat. This function is used in an upcoming Lesson where knowing the sign of an integer plays an important role.