C :: Y / N Option To Continue - Compiler Does Not Read It As A Loop

I've been having problems with my loop that asks if the user wishes to continue or not. The required input should either be 'y' or 'Y', or 'n' or 'N'. Anything else should be counted as invalid, and repeat the prompt for input. The first few times I ran my program, the compiler does not read it as a loop. The next few times just won't work properly.

Here is the prompt:
Code:
void question() {
char option;
printf("
Do you want to continue? {Y|N) ");
scanf("%c", &option);

[Code] ......

As it is, it immediately runs the else option, but otherwise runs just fine. I suspect it could be because I have not specified a size for the option variable, but I try doing that, and the prompt relegates everything to the else.

(And also, here's the rest of the code. Basically, it just assigns a value to the letters of the word (a/A = 1, b/B = 2, etc.), adds these values, and determines if a word is prime or not based on the sum.)

Code:
#include <stdio.h>
#include <string.h>
#define size 30
int main() {
char letter, word[size], lower, upper, option;
int i, value, ans = 0, a, choice = 1;

[Code] .....