Calculator in C++

Question

I made a calculator in C++. I wanted to ask is this code well written, understandable, and alright.

#include <iostream>
using namespace std;

int main() {
        // Declares the variable to store the asked value
        int num1, num2;
        char op;
        // Asks the user for the input of numbers and the operation
        cin >> num1;
        
        cin >> op;
        
        cin >> num2;
        // Declares a variable for the answer
        int result;
  // Handles all the conditions of the operation
  if(op == '+') {
    result = num1 + num2;
} else if(op == '-'){
    result = num1 - num2;
} else if(op == '*') {
    result = num1 * num2;
} else if(op == '/') {
    result = num1 / num2;
} else {
    cout << "Invalid values";
    cout<<endl<<endl;
}
    // Outputs the result
    cout << "Answer: ";
    cout << result;
    // Ouputs a thankyou message
    cout<<endl<<endl;
    cout << "THANKS FOR USING THIS";
    return 0;
}

Answer 1

I have some suggestions here:

1. Using switch/case instead of if/else looks a little better and slightly faster as also mentioned in the comments.

2. You could definitely work on formatting your code it can be a lot better

Answer 2

A good next step in your code would be to test edge cases and account for them. A couple things you could improve:

1. Your code does not handle division by zero. If someone puts in 1 / 0 your program will crash. You can check for this and give the user a nice error message

2. Your code does not handle integer overflow. You'll get interesting results if you try to do 2000000000 * 2000000000 because an int can only hold so large of a value.

Answer 3

Switch/Case over if/else

I think it would be great if you use switch/case instead of if/else it also makes you code look neat. Something like this

switch(op)
    {
      case '+': result = num1 + num2;    break;
      case '-': result = num1 - num2;    break;
      case '*': result = num1 * num2;    break;
      case '/': result = num1 / num2;    break;
      default:
          cout << "Please enter valid operation" ;
    }

Moreover, using switch/cases over if/else improves computational time when doing multiple iterations.

Add an OFF button

Also, the physical calculators that we use are always 'ON' unless they are turned off by pressing an 'OFF' button (or get turned off if no key is pressed for time \$t\$). You can also add that feature.

Instruction: type of input expected form user.

Say, a friend of yours wants to run the code, or you are an app developer and your client do not know anything about programming, and he just double-clicks on calculator.exe file, it would be great if you can also mention a short note when the program begins telling what logical operations and input format is expected from the user.

Showing error message

When someone types in num1 / 0. You can either show the error message

cout << DIVIDE_BY_ZERO_ERROR << endl;

Or simply say the answer in Infinity. And its value is

#include <limits>
// ...

double a = std::numeric_limits<double>::infinity();

You do not need to show this value, just in case if you want to take this code further and add some more features like 'memory' like our typical calculators. Note: this is not real infinity! It just a number such that \$a>b\,\,\forall b\$. There is more about Handling the Divide by Zero Exception in C++. Perhaps, I have given only a short glimpse sticking with minimal code policy.

Answer 4

Prefer switch over else ifs

Switch will make your code easier to read.

The variable result could be uninitialized

Consider situation where user types in incorrect operator. In this case the result is uninitialized and your calculator crashes.

Division by zero crashes

Prefer \n over endl

The endl forces the stream to flush. Instead of

cout << "Answer: ";
cout << result;
// Outputs a thankyou message
cout << endl << endl;
cout << "THANKS FOR USING THIS";

I would suggest something like

std::cout << "Answer: " << result 
    << "\n\nTHANKS FOR USING THIS\n";