CODEWITHSUNDEEP
c
user8867549
user8867549

Reputation:

How to only allow specific Input in C

My Code:

#include<stdio.h>
char checkInput0(void);

int main() {
   char output;
   output = checkInput0();
   printf("The output is %c", output);
}

char checkInput0(void){
    char option0 = '\0',check0;
    char c;

    do{
        printf("Please enter your choice: ");

         if(scanf("%c %c",option0, &c) != 'A' || c != 'B' ){
            while((check0 = getchar()) != 0 && check0 != '\n' && check0 != EOF);
            printf("[ERR] Please enter A or B.\n");
        }else{
            break;
        }
    }while(1);
    return option0;
}

I would like to only allow the user to input only "A" or "B" and if anything else would be entered I would like to reprompt the user with the following message: [ERR] Please enter A or B.\n

I have written a funktion which worked with numbers but I can't get the one above (checkInput0) to work, what have I done wrong

Upvotes: 0

Views: 1090

Answers (1)

Bathsheba
Bathsheba

Reputation: 234635

  1. scanf does not return c, it returns the number of variables successfully set. Comparing that to 'A' is pretty pointless.

  2. Change your scanf call to scanf("%c %c", &option0, &c): currently the behaviour is undefined: the variable arguments need to be pointer types.

  3. x != 'A' || x != 'B' is 1 for any value of x.

Consider moving scanf outside the if conditional: checking the return value of scanf explicitly. On the third point, did you want &&?

Also be careful with ace code that writes c on one side of an operator, and reads it on the other. It's fine in this instance since || is a sequencing point, but you are quite close to undefined behaviour here.

Upvotes: 2

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