Question

My functions:

//Check Character Case(Upper/Lower Case). If Upper Convert to Lower Case.
char checkLetterCase(char letter){
    if(letter >= 65 && letter <= 90){
        letter = tolower(letter);
        return letter;
    }
    else if(letter >= 97 && letter <= 122){
        return letter;
    }
    else{
        return 0;
    }
}

//Add the Specified Letter by Creating a New Node in the Letter List defined
void addLetter(letterListT *letListHead, char letter){
    letterListT *newNode;
    newNode = (letterListT *)malloc(sizeof(letterListT));

    //Check Case(lowe/upper)
    letter = checkLetterCase(letter);  

    //This may only occur on user input
    while(letter == 0){
        printf("Guess a letter: ");
        scanf("%c", &letter);
        letter = checkLetterCase(letter);
    }

     newNode->letter = letter;

    newNode->nxt = letListHead->nxt;
    letListHead->nxt = newNode;
}

My call in main:

addLetter(unusedLetList, i=0);

and this is my outpun on run:

Guess a letter: 6
Guess a letter: Guess a letter: t 

and my question is: why when i put a non character i get the “Guess a letter” message twice?

Answer 1

Because after pressing <enter>, there’s an extra newline character that is not (yet) consumed by scanf(). Make a call to getchar() to get rid of that:

letter = checkLetterCase(letter);
if (letter == 0) getchar();

By the way, your checkLetterCase() function is broken on non-ASCII systems. Use this instead:

#include <ctype.h>

char checkLetterCase(char letter)
{
    return isalpha(letter) ? letter : 0;
}