Question

I am trying to understand C, by going through K&R. I have trouble understanding this code for two functions found in the book:

void qsort(int v[], int left, int right){
int i, last;

void swap(int v[], int i, int j);

if (left >= right)
    return;

swap(v, left, (left+right)/2);

last = left;

for ( i = left+1; i<=right; i++)
    if (v[i]<v[left])
        swap(v,++last, i);

swap(v,left,last);
qsort(v,left,last-1);
qsort(v,last+1,right);
}


void swap(int v[], int i, int j){

    int temp;

    temp = v[i];
    v[i] = v[j];
    v[j] = temp;
}

These two function perform a quicksort on a given array. In the main function I created an int array and called qsort. It compiled fine and ran fine. My question is, why is the prototype for swap() put in the function qsort() and not before main()?

Answer 1

The prototype should be added before the actual function is used for first time.
In this case, I do not think its a general practice to have prototype in qsort() function, however, it still serves the purpose. The prototype for swap() could also be added before main() too, don’t think it will make a difference.