I need help writing a Loop that finds vowels in C-CodePudding

I need to prompt the user for a letter. If that letter is not a vowel, keep prompting until a vowel is entered.

My desired outcome is:

Enter a vowel:z

That is not a vowel. Try again:h

That is not a vowel. Try again:w

That is not a vowel. Try again:t

That is not a vowel. Try again:o

Congrats. You picked a vowel.

So far my code is:

do 
{
printf("Enter a vowel: ");
scanf(" %c", &letter);
}

while (letter != 'a' && letter != 'e' && letter != 'i' && letter != 'o' && letter != 'u' && letter != 'A' && letter != 'E' && letter != 'I' && letter != 'O' && letter != 'U');
{
printf("That is not a vowel. Try again: ");
scanf(" %c", &letter);    
}

printf("Congrats. You picked a vowel!!!");

CodePudding user response：

Do and While should go together. So you are looking for a code that will be something like below. Your objective should be to ensure the user is in loop till a vowel is received. Also you can further improve the code by using functions for the vowel check. Find a sample below.

    do 
    {
        printf("Enter a vowel: ");
        scanf(" %c", &letter);
        if (letter != 'a' && letter != 'e' && letter != 'i' && letter != 'o' && letter != 'u' && letter != 'A' && letter != 'E' && letter != 'I' && letter != 'O' && letter != 'U')
            printf("Sorry, Try again \n");
    } while (letter != 'a' && letter != 'e' && letter != 'i' && letter != 'o' && letter != 'u' && letter != 'A' && letter != 'E' && letter != 'I' && letter != 'O' && letter != 'U');
    
    printf("Congrats. You picked a vowel!!!");
    }

The applicable loops in C are do-while, for and while. There is no do.

CodePudding user response：

Your braces, indentation and spacing are deceptive. It looks like the do has no while and that the while controls the block below it...

Try this:

/*...*/
    while( 1 ) {
        printf( "Enter a vowel: " );

        char letter;
        if( scanf( " %c", &letter ) != 1 )
            exit( -1 );

        if( strchr( "aeiouAEIOU", letter ) != NULL ) // found!
            break;

        printf( "That is not a vowel. Try again:\n\n" );
    }
    printf( "Congrats. You picked a vowel!!!\n" );
    // NB: 'letter' has "gone out of scope".
/*...*/

strchr() searches the string supplied for a matching character, returning NULL if it is NOT found (ie: not a vowel, in this case.)

The "infinite loop" can only "break" when the user supplies a vowel.

Add a few LFs (\n) to the print statements.

CodePudding user response：

Hopefully OP will see the problem once OP's code is properly formatted.

  do {
    printf("Enter a vowel: ");
    scanf(" %c", &letter);
  } while (letter != 'a' && letter != 'e' && letter != 'i' && letter != 'o'
      && letter != 'u' && letter != 'A' && letter != 'E' && letter != 'I'
      && letter != 'O' && letter != 'U');

  {
    printf("That is not a vowel. Try again: ");
    scanf(" %c", &letter);
  }

There is no error message in the loop.

CodePudding user response：

A more concise way to achieve that would be using strchr(), as suggested by @tadman in the comments.

#include <stdio.h>
#include <string.h>

int main () {
    char * vowels = "aeiouAEIOU";
    char letter;
    do {
        printf("Enter a vowel: ");
        scanf(" %c", &letter);
    } while (strchr(vowels, letter) == NULL);

    printf("Congrats. You picked a vowel!!!");
}