qsort.c

#include <stdio.h>

void qsort(int *X, int L, int U) {
    int T, M, i, tmp;
    if (L < U) {
        T = X[L];
        M = L;
        for (i = L+1; i < U; i++) {
            if (X[i] < T) {
                M += 1;
                tmp = X[M];
                X[M] = X[i];
                X[i] = tmp;
            }
        }
        X[L] = X[M];
        X[M] = T;
        qsort(X, L, M);
        qsort(X, M+1, U);
    }
}


int main(int argc, char *argv[]) {
    int a[] = {4, 65, 2, -31, 0, 99, 2, 83, 782, 1};
    int n = sizeof a / sizeof a[0];
    int i;
    for (i = 0; i < n; i++)
        printf("%d%s", a[i], i == n - 1 ? "\n" : " ");
    qsort(a,0, n);
    for (i = 0; i < n; i++)
        printf("%d%s", a[i], i == n - 1 ? "\n" : " ");
    return 0;
}