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

// _pow(n, exponent) should return n^exponent, for exponent ≥ 1
int _pow(int n, int exponent) { // buggy power function
    int result = 0; // BUG: 0→1 // *should* return n^exponent
    for(int i = 0; i < exponent; i++) {
        result *= n;
    }

    // Note:  This is an extreme use of assert(…).  Normally, you would
    //        have only 1-2 at a time.
    //
    // This demonstration was fleshing out different ways of expressing the
    // "post-conditions" (things you expect to be true before program exits)
    // using assert(…).

    assert(! (n >  0 && result <= 0));
    assert(! (n == 0 && result != 0));
    assert(! (n <  0 && exponent % 2 == 0 && result < -n));
    assert(! (n <  0 && exponent % 2 == 1 && result >  n));

    assert(! (exponent == 0 && n != 0 && result != 1));
    assert((n >  0 && result >= n) ||
           (n == 0 && result == 0) ||
           (n <  0 && exponent % 2 == 0 && result >= -n) ||
           (n <  0 && exponent % 2 == 1 && result <=  n));
    assert(! (result < n && n >= 0));
    return result;

    // OPTIONAL:  For more on logic, see De Morgan's Laws
    //            https://en.wikipedia.org/wiki/De_Morgan%27s_laws
}

int main(int argc, char* argv[]) {
    int n2 = _pow(5, 2);
    printf("5 ^ 2 == %d\n", _pow(5, 2));
    return EXIT_SUCCESS;
}


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