Question

How to check whether a number is positive/zero/negative without using conditional statements in C

Answer 1

#include <stdio.h>

int main() {
    int n = 89;

    // create text labels for each possible case
    const char* result[3] = {
        "negative",  // index 0
        "zero",      // index 1
        "positive"   // index 2
    };

    // compute an index without using any conditional statements
    // (n > 0) becomes 1 if true, 0 if false
    // (n < 0) becomes 1 if true, 0 if false
    // index = 1 + (n > 0) - (n < 0)
    int index = 1 + (n > 0) - (n < 0);

    // print the classification
    printf("%s\n", result[index]);

    /*
       Checks:

       n = -3
       (n > 0) = 0
       (n < 0) = 1
       index = 1 + 0 - 1 = 0
       result = negative

       n = 0
       (n > 0) = 0
       (n < 0) = 0
       index = 1 + 0 - 0 = 1
       result = zero

       n = 89
       (n > 0) = 1
       (n < 0) = 0
       index = 1 + 1 - 0 = 2
       result = positive
    */

    return 0;
}


/*
run:

positive

*/

 

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