#include <stdio.h>

int main(int argc, char *argv[]){

    if(argc != 2){
        printf("You must supply one argument!\n");
        //this is how you abort a program.
        return 1;
    }

    return 0;
}
#include <stdio.h>

int main(int argc, char *argv[]){

    if(argc != 2){
        printf("You must supply 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;
            default:
                printf("%d:%c is not a vowel.\n",i,letter);
        }
    }

    return 0;
}
Switch on vowels in argument
Switch on vowels in argument
