Joel Coding Problem reverse_string

#include <stdio.h>
#include <string.h>
void reverse_string(char* str) {
  int end_i = strlen(str) - 1;
  for (int start_i = 0; start_i < end_i; start_i++, end_i--) {
    int temp  = str[end_i];
    str[end_i] = str[start_i];
    str[start_i] = temp;
  }
}

int main(int argc, char* argv[]) {
  if (argc < 2) {
    printf("%s {string}\n", argv[0]);
    return 0;
  }

  printf("%s\n", argv[1]);
  reverse_string(argv[1]);
  printf("%s\n", argv[1]);

  return 0;
}