[C] printf/scanf in loop problem

programming
1 
#include <stdio.h>
int a,b;
int add(a,b){
    int sum = a+b;
    return(sum);
}
int sub(a,b){
    int diff = a-b;
    return(diff);
}
int mult(a,b){
    int prod = a*b;
    return(prod);
}
int div(a,b){
    int quot = a/b;
    return(quot);
}
int rem(a,b){
    int rem = a%b;
    return(rem);
}
main()
{
    int x,y,ans;
    char op;
    while(op!='x'||op!='X'){
        printf("
[A] Addition
** Subtraction
[c] Multiplication
[D] Division
[E] Remainder
");
        printf("
Which operation? ");
        scanf("%c",&op);
        if(op=='a'||op=='A'){
            printf("
Input 1st no: ");
            scanf("%d",&x);
            printf("Input 2nd no: ");
            scanf("%d",&y);
            ans = add(x,y);
            printf("
Answer is: %d
",ans);

        }else if(op=='b'||op=='B'){
            printf("Input 1st no: ");
            scanf("%d",&x);
            printf("Input 2nd no: ");
            scanf("%d",&y);
            ans = sub(x,y);
            printf("
Answer is: %d
",ans);
    
        }else if(op=='c'||op=='C'){
            printf("Input 1st no: ");
            scanf("%d",&x);
            printf("Input 2nd no: ");
            scanf("%d",&y);
            ans = mult(x,y);
            printf("
Answer is: %d
",ans);
        
        }else if(op=='d'||op=='D'){
            printf("Input 1st no: ");
            scanf("%d",&x);
            printf("Input 2nd no: ");
            scanf("%d",&y);
            ans = div(x,y);
            printf("
Answer is: %d
",ans);
        
        }else if(op=='e'||op=='E'){
            printf("Input 1st no: ");
            scanf("%d",&x);
            printf("Input 2nd no: ");
            scanf("%d",&y);
            ans = rem(x,y);
            printf("
Answer is: %d
",ans);
        
        }else if(op=='x'||op=='X'){
            break;
        }else{
            printf("
Try again
");
        
        }
    }
    printf("
**Program Terminated**
");
}

we were given an assignment in class today. in the above code, i am trying to achieve where a user chooses an operation(a,b,c,d,e), and inputs 2 numbers and outputs the answers. it works fine but after the first loop, the first 3 lines of the loop are executed twice… :puzzled:
why is this and how do i fix it? :book: