Making simple calculator in C - c

Question

I'm making a simple calculator in C with operators +-*/. I tried to make a calculator but I have some problem with using do..while. I think while (op != 'A', 'Q', 'M', 'D', 'S'); is incorrect. What should I require here?
#include<stdio.h>
int main(void)
{
int x, y, result;
char op;
printf("****************\n");
printf("A-----Add\n");
printf("S-----Substract\n");
printf("M-----MUltiply\n");
printf("D-----Divide\n");
printf("Q-----Quit\n");
printf("****************\n");
printf("Enter the operation:");
scanf("%c", &op);
printf("Enter the two variables:");
scanf("%d %d", &x, &y);
do {
if (op == 'A')
result = x + y;
else if (op == 'S')
result = x - y;
else if (op == 'M')
result = x*y;
else if (op == 'D')
result = x / y;
else if (op == 'Q')
break;
} while (op != 'A', 'Q', 'M', 'D', 'S');
printf("%d %c %d = %d\n", x, op, x, result);
return 0;
}

Answer 1

!= is a binary operator, it takes one value on the left and one value on the right. You can't compare multiple values at once by just listing several values on the right.
To get this code working with minimal changes, you can compare op to each the variables individually, and combine them using the standard logical operators (e.g. &&).
You also need to think about the logic of your code. You're using a do ... while loop, which means that code will run at least once, and each time it reaches the end it will run again if the while condition is true. What happens after its first run? What happens if the user input (op) is none of the options specified? And you've got a 'quit' option, but what happens when it's used?

Answer 2

Four issues:
This: while (op != 'A', 'Q', 'M', 'D', 'S') doesn't do what you expect. You need to compare op against each value individually and do a logical AND (&&) between them.
If you don't enter a proper letter, your while loop will be an infinite loop because the prompt for user data is outside of the loop instead of inside. Move the printf and scanf calls to the inside of the loop.
If you do get an invalid input, the newline pressed by the user will get read in as the value to the first scanf. Put a blank space at the beginning of each scanf pattern to eat any newlines that may be in the buffer.
When you're printing the result, you're printing x as the second operand instead of y.
When you apply the above, you should have this:
#include<stdio.h>
int main(void)
{
int x, y, result;
char op;
printf("****************\n");
printf("A-----Add\n");
printf("S-----Substract\n");
printf("M-----MUltiply\n");
printf("D-----Divide\n");
printf("Q-----Quit\n");
printf("****************\n");
do {
// these four lines go inside the loop to prompt again
printf("Enter the operation:");
scanf(" %c", &op); // the space at the start eats the newline
printf("Enter the two variables:");
scanf(" %d %d", &x, &y); // the space at the start eats the newline
if (op == 'A')
result = x + y;
else if (op == 'S')
result = x - y;
else if (op == 'M')
result = x*y;
else if (op == 'D')
result = x / y;
else if (op == 'Q')
break;
// compare op against each value individually
} while (op != 'A' && op != 'Q' && op != 'M' && op != 'D' && op != 'S');
printf("%d %c %d = %d\n", x, op, y, result);
return 0;
}

Answer 3

while (op != 'A' && op != 'Q' && op !='M' && op !='D' && op !='S');