C/Console/Console Input Validation

  
#include <stdio.h>
int main(void)
{
  int a, b;
  char ch;
  printf("Do you want to (Choose the first letter):\n");
  printf("(A)dd, (S)ubtract, (M)ultiply, or (D)ivide?\n");
  do {
    printf("Choice: ");
    ch = getchar();
  } while(ch!="A" && ch!="S" && ch!="M" && ch!="D");
  printf("\n");
  printf("Enter first number: ");
  scanf("%d", &a);
  
  printf("Enter second number: ");
  scanf("%d", &b);
  if(ch=="A") 
      printf("%d", a + b);
  else if(ch=="S") 
      printf("%d", a - b);
  else if(ch=="M") 
      printf("%d", a * b);
  else if(ch=="D" && b!=0) 
      printf("%d", a / b);
  return 0;
}