#include<stdio.h>

int StringToInt();
void Calculate(int n1,int n2,char op);

int main(){
  
    int n1,n2;
	char c,op;

    printf("Enter any integer as a string: ");

   n1 = StringToInt(); // convert first num
   op = getchar(); // read the operator  
   n2 = StringToInt();    

   Calculate(n1,n2,op)

    return 0;
}

int StringToInt()
{

int i=0,sum=0;
	
while(isspace(c = getchar()); // skipping spaces
    
	do
	{
         if(c < 48 || c > 57)
		 {
             printf("Unable to convert it into integer.\n");
             return 0;
         }
         else
		 {
             sum = sum*10 + (c - 48);             
         }
		 
    } while(!isspace(c = getchar()) || c != '\n') // in the end of the function c contains the space between first num and operator

    return sum;
}

void Calculate(int n1,int n2,char op)
{	
	switch(op)
	{
		case '+' : printf("\n%d + %d = %d",n1,n2,n1+n2); break;
		case '-' : printf("\n%d - %d = %d",n1,n2,n1-n2); break;
		case '*' : printf("\n%d * %d = %d",n1,n2,n1*n2); break;
		case '/' : printf("\n%d / %d = %d",n1,n2,n1/n2); break;
		default: printf("invalid operator %c",op);
	}
}