Swap and Sort

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
void swap(char *string) {
  for (int i = 0; string[i]; i++) {
    char c = string[i];
    if (islower(c)) string[i] = toupper(c);
    else if (isupper(c)) string[i] = tolower(c);
  }
}
void sort(char *string, int left, int right) {
  if (left >= right) return;
  int i = left, j = right;
  char tmp, pivot = string[rand() % (j - i) + i];
  while (1) {
    while (string[i] < pivot)
      i++;
    while (string[j] > pivot)
      j--;
    if (i >= j) break;
    tmp = string[i];
    string[i] = string[j];
    string[j] = tmp;
    i++;
    j--;
  }
  sort(string, left, i - 1);
  sort(string, j + 1, right);
}
int main(void) {
  char string[] = "cbaZYXcbaZYX";
  printf("Original: %s\n", string);
  swap(string);
  printf("Swap: %s\n", string);
  sort(string, 0, strlen(string) - 1);
  printf("Sort: %s\n", string);
  return 0;
}