toupper function doesn't work with pointer dereference?

Question

I am writing a program that determines whether the input is white or sweet bread, and I pass the value that determines the bread type to a function as a pointer:

#include <ctype.h>

void WhiteSweetChoosing(char *orWhiteSweet);

int main(){

    char orWhiteSweet ,isDouble, isManual;
    WhiteSweetChoosing(&orWhiteSweet);
    printf("%c", orWhiteSweet);

    return 0;
}

void WhiteSweetChoosing(char *orWhiteSweet){
    printf("Please enter your bread type\n");
    printf("W for white and S for sweet:");
    scanf(" %c", orWhiteSweet);
    *orWhiteSweet = toupper(*orWhiteSweet);

    while(*orWhiteSweet != 'S' && *orWhiteSweet != 'W'){
        printf("Please enter valid character\n");
        printf("W for white and S for sweet:");
        scanf(" %c", orWhiteSweet);
    }

}

However, this doesn't work as the toupper function doesn't seem to assign the new value to the dereferenced pointer. I have put one printf under the function to verify that toupper doesn't work.

But when I assign the value to a new variable instead of the old dereferenced pointer itself, it started to work:

void WhiteSweetChoosing(char *orWhiteSweet){
    printf("Please enter your bread type\n");
    printf("W for white and S for sweet:");
    scanf(" %c", orWhiteSweet);
    char WorS = toupper(*orWhiteSweet);

    while(WorS != 'S' && WorS != 'W'){
        printf("Please enter valid character\n");
        printf("W for white and S for sweet:");
        scanf(" %c", orWhiteSweet);
        WorS = toupper(*orWhiteSweet);
    }

}

I would be appreciated if someone is kind enough to explain why, thanks

Answer 1

You forget to apply toupper for values read by second or later scanf() .

void WhiteSweetChoosing(char *orWhiteSweet){
    printf("Please enter your bread type\n");
    printf("W for white and S for sweet:");
    scanf(" %c", orWhiteSweet);
    *orWhiteSweet = toupper(*orWhiteSweet);

    while(*orWhiteSweet != 'S' && *orWhiteSweet != 'W'){
        printf("Please enter valid character\n");
        printf("W for white and S for sweet:");
        scanf(" %c", orWhiteSweet);
        *orWhiteSweet = toupper(*orWhiteSweet); /* add this */
    }

}