4. Program should ask the user to enter a number, an operator, and another number. It should then carry out the specified arithmetical operation: adding, subtracting, multiplying, or dividing the two numbers. Finally, display the result.

Chapter 3: 

Loops and Decisions

Programming Exercise

Problem # 4:

Create the equivalent of a four-function calculator. The program should ask the user to enter a number, an operator, and another number. (Use floating point.) It should then carry out the specified arithmetical operation: adding, subtracting, multiplying, or dividing the two numbers. Use a switch statement to select the operation. Finally, display the result.
When it finishes the calculation, the program should ask whether the user wants to do another calculation. The response can be ‘y’ or ‘n’. Some sample interaction with the program might look like this:
Enter first number, operator, second number: 10 / 3
Answer = 3.333333
Do another (y/n)? y
Enter first number, operator, second number: 12 + 100
Answer = 112
Do another (y/n)? n

Solution:

#include <iostream>
using namespace std;
#include <conio.h>
int main()
{
    char op, i;
    float num1, num2, ans;
  
    start:
        cout<<"Enter first number, operator, second number: ";
        cin>>num1>>op>>num2;
        switch(op)
        {
            case '+':
            ans=num1+num2;
            break;
            case '-':
                ans=num1-num2;
                break;
            case '*':
                ans=num1*num2;
                break;
            case '/':
                ans=num1/num2;
                break;
            default:
                cout<<"Invalid input.";
        }
      
        cout<<"Answer = "<<ans<<endl;
        cout<<"Do another (y/n)? ";
        i=getche();
        cout<<endl;
      
    if(i=='y')
        goto start;
      
    return 0;
}

Let me know in the comment section if you have any question.

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