#include <stdio.h>
#include <stdlib.h>

int main()
{
		double num1;
		double num2;
		char op;
		
		printf("Enter a number: ");
		scanf("%lf", &num1);
		printf("Enter operator: ");
		scanf(" %c", &op);   // %c 전에 항상 space 넣어야됨!
		printf("Enter a anumber: ");
		scanf("%lf", &num2);

		if(op == '+'){
				printf("%f", num1 + num2);
		} else if(op == '-'){
				printf("%f", num1 - num2);
		} else if(op == '/'){
				printf("%f", num1 / num2);
		} else if(op == '*'){
				printf("%f", num1 * num2);
		} else{
				printf("Invalid Operator");
		}
				
		return 0;
}

Case 0: Success!

Case 1: Invalid Operator