ex13.c

#include <stdio.h>

int main(int argc, char *argv[])
{
  if (argc != 2) {
    printf("ERROR! You ned one argument.\n");
    // this is how you abort a program
    return 1;
  }

  int i = 0;
  for (i = 0; argv[1][i] != '\0'; i++) {
    char letter = argv[1][i];
    
    switch(letter) {
      case 'a':
      case 'A':
        printf("%d: 'A'\n", i);
        break;

      case 'e':
      case 'E':
        printf("%d: 'E'\n", i);
        break;

      case 'i':
      case 'I':
        printf("%d: 'I'\n", i);
        break;

      case 'o':
      case 'O':
        printf("%d: 'O'\n", i);
        break;

      case 'u':
      case 'U':
        printf("%d: 'U'\n", i);
        break;

      case 'y':
      case 'Y':
        if(i > 2) {
          // it's only sometimes Y
          printf("%d: 'Y'\n", i);
        }
        break;
      
      default:
        printf("%d: %c is not a vowel\n", i, letter);
    }
  }

  return 0;
}