C++ Program to Create Simple Calculator

A simple calculator in C++ can be created by taking two numbers and an operator as input, then using switch to perform +, -, *, or / operations, like: switch(op) { case '+': result = num1 + num2; break; ... }.

Examples

Input5 + 3

OutputResult: 8

Input10 / 2

OutputResult: 5

Input7 * 0

OutputResult: 0

How to Think About It

To build a simple calculator, first get two numbers and an operator from the user. Then check which operator was entered using switch or if statements. Perform the matching arithmetic operation and show the result. Handle division carefully to avoid dividing by zero.

Algorithm

1

Get the first number from the user

2

Get the operator (+, -, *, /) from the user

3

Get the second number from the user

4

Use a switch or if-else to check the operator

5

Perform the corresponding arithmetic operation

6

Display the result to the user

Code

cpp

#include <iostream>
using namespace std;

int main() {
    double num1, num2, result;
    char op;
    cout << "Enter first number: ";
    cin >> num1;
    cout << "Enter operator (+, -, *, /): ";
    cin >> op;
    cout << "Enter second number: ";
    cin >> num2;

    switch(op) {
        case '+': result = num1 + num2; break;
        case '-': result = num1 - num2; break;
        case '*': result = num1 * num2; break;
        case '/':
            if (num2 != 0) result = num1 / num2;
            else {
                cout << "Error: Division by zero!" << endl;
                return 1;
            }
            break;
        default:
            cout << "Invalid operator" << endl;
            return 1;
    }

    cout << "Result: " << result << endl;
    return 0;
}

Output

Enter first number: 5
Enter operator (+, -, *, /): +
Enter second number: 3
Result: 8

Dry Run

Let's trace the input '5 + 3' through the code

1

Input first number

num1 = 5

2

Input operator

op = '+'

3

Input second number

num2 = 3

4

Check operator and calculate

op is '+', so result = 5 + 3 = 8

5

Output result

Print 'Result: 8'

Step	Variable	Value
1	num1	5
2	op	+
3	num2	3
4	result	8

Why This Works

Step 1: Input collection

The program asks the user for two numbers and an operator using cin to read input.

Step 2: Operator selection

The switch statement checks the operator and selects the matching arithmetic operation.

Step 3: Calculation and output

The program performs the calculation and prints the result with cout. It also handles division by zero to avoid errors.

Alternative Approaches

Using if-else instead of switch

cpp

#include <iostream>
using namespace std;

int main() {
    double num1, num2, result;
    char op;
    cout << "Enter first number: ";
    cin >> num1;
    cout << "Enter operator (+, -, *, /): ";
    cin >> op;
    cout << "Enter second number: ";
    cin >> num2;

    if (op == '+') result = num1 + num2;
    else if (op == '-') result = num1 - num2;
    else if (op == '*') result = num1 * num2;
    else if (op == '/') {
        if (num2 != 0) result = num1 / num2;
        else {
            cout << "Error: Division by zero!" << endl;
            return 1;
        }
    } else {
        cout << "Invalid operator" << endl;
        return 1;
    }

    cout << "Result: " << result << endl;
    return 0;
}

This approach uses if-else statements which some find easier to read but can be longer for many cases.

Using functions for each operation

cpp

#include <iostream>
#include <stdexcept>
using namespace std;

double add(double a, double b) { return a + b; }
double subtract(double a, double b) { return a - b; }
double multiply(double a, double b) { return a * b; }
double divide(double a, double b) {
    if (b == 0) throw runtime_error("Division by zero");
    return a / b;
}

int main() {
    double num1, num2, result;
    char op;
    cout << "Enter first number: ";
    cin >> num1;
    cout << "Enter operator (+, -, *, /): ";
    cin >> op;
    cout << "Enter second number: ";
    cin >> num2;

    try {
        switch(op) {
            case '+': result = add(num1, num2); break;
            case '-': result = subtract(num1, num2); break;
            case '*': result = multiply(num1, num2); break;
            case '/': result = divide(num1, num2); break;
            default:
                cout << "Invalid operator" << endl;
                return 1;
        }
        cout << "Result: " << result << endl;
    } catch (const exception& e) {
        cout << "Error: " << e.what() << endl;
        return 1;
    }
    return 0;
}

This approach organizes code better by separating operations into functions and uses exception handling for errors.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a fixed number of operations regardless of input size, so it runs in constant time O(1).

Space Complexity

It uses a fixed amount of memory for variables and no extra data structures, so space complexity is O(1).

Which Approach is Fastest?

All approaches run in constant time; using functions adds slight overhead but improves readability and maintainability.

Approach	Time	Space	Best For
Switch statement	O(1)	O(1)	Simple and clear operator selection
If-else statements	O(1)	O(1)	Easier for beginners with few operators
Functions with exception handling	O(1)	O(1)	Better code organization and error handling