Switch Statement with Array condition - c

Question

I am having an impossible time trying to make this work. It is just a sample run of the code without the full options.
What is needed from the program is for the user to enter there choice, 1-3 or a-c. I am using a string in case the user enters more than just a single character. The switch case then should compare just the first char in the array to the cases. And the do while loop is to make sure it keeps going until they enter the right characters.
#include <stdio.h>
#define SIZE 81
void main(){
char thing[SIZE] = {3};
int rvalue;
do
{
scanf_s("%s", thing);
switch (thing[0])
{
case 'a':
case 1:
printf("first\n");
rvalue = 1;
break;
case 'b':
case 2:
printf("second\n");
rvalue = 2;
break;
case 'c':
case 3:
printf("third\n");
rvalue = 3;
break;
default:
printf("Wrong\n");
rvalue = 4;
break;
}
} while (rvalue == 4);
}

Answer 1

Change
scanf_s("%s", thing);
To
scanf_s("%s", thing,(unsigned int)sizeof(thing)); //Read the comments to know why the cast is required
This done because scanf and scanf_s are different function. scanf_s has an additional argument present to prevent buffer overflows.
Also change these
case 1:
case 2:
case 3:
To
case '1':
case '2':
case '3':
Because the character 1('1') and the rest of them are different from the integer 1. The characters(those enclosed in single quotes) have their values represented in the ASCII table.

Answer 2

As far as it seems, you want to print first when the first character in the thing string is a or 1, and so on.
The problem is that case 1: is not same as case '1':. 1 is an int, '1' is a char, and as you are comparing the first character of the string, you need to change your casestatements a bit.
Code:
#include <stdio.h>
#define SIZE 81
void main(){
char thing[SIZE] = {3};
int rvalue;
do
{
scanf_s("%s", thing,SIZE);
switch (thing[0])
{
case 'a':
case '1':
printf("first\n");
rvalue = 1;
break;
case 'b':
case '2':
printf("second\n");
rvalue = 2;
break;
case 'c':
case '3':
printf("third\n");
rvalue = 3;
break;
default:
printf("Wrong\n");
rvalue = 4;
break;
}
} while (rvalue == 4);
}