Immediate break after input using switch or if

I am learning C right now and im at the very beginning.

Here's my code:

#include <stdio.h>

int main (){

char operator;
double num1;
double num2;
double result;

printf("\n Enter an operator");
scanf("%c", &operator);

printf("Enter number 1:");
scanf("%lf", &num1);

printf("Enter number 2:");
scanf("%lf", &num2);


switch(operator){
    break;
    case '+':
        result = num1 + num2;
        printf("\nresult: %.0lf", result);
        break;
      case '-':
        result = num1 - num2;
        printf("\nresult: %.0lf", result);
        break;
      case '*':
        result = num1 * num2;
        printf("\nresult: %.0lf", result);
        break;
      case '/':
        result = num1 / num2;
        printf("\nresult: %lf", result);
        break;
    default:
       printf("%c is not valid", operator);
}
    return 0;
}

If I enter an operator other than / / * + or -, I get 'x is not valid' after entering the numbers, so I need your help with this. If I enter the wrong operator at the very beginning, how do I end the code right there so I don't have to enter that number?

I thought of using break func. or if-else but, I am not able to do that.

Thanks for your help!

I want the code to immediately display the 'wrong operator' error if I enter the wrong operator.

I thought of using break func. or if-else but, I am not able to do that.

Are you allowed to use any if statements? Or is it simply that you cant use an if-else to check if input operator equals each of valid operator separately?

If you can use one if statement you can use strchr(), which checks if a character (input) is found in a string (valid operators):

const char *valid_chars = "//*+-";
printf("\n Enter an operator");
scanf("%c", &operator);

if (!strchr(valid_chars, operator)) {
     printf("Wrong operator");
}