caution

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Simple calculator

Requires knowledge of: 1. First program - 4. Conditions

Overview

A simple program that allows you to calculate:

• ➕ a sum
• ➖ a difference
• ✖ a product
• ➗ a quotient

of two real numbers.

Source code

#include <iostream>

int main()
{
	std::cout	<< "=== CALCULATOR ===\n"
				<< "Menu:\n"
				<< "1) Add\n"
				<< "2) Subtract\n"
				<< "3) Multiply\n"
				<< "4) Divide\n"
				<< "> Your choice: ";

	int choice;
	std::cin >> choice;

	float a, b;
	if (choice == 1)
	{
		std::cout	<< "Calculating a sum (a + b).\n"
					<< "Please enter the first number: ";
		std::cin >> a;

		std::cout	<< "Please enter the second number: ";
		std::cin >> b;

		std::cout << "a + b equals " << (a + b);
	}
	else if (choice == 2)
	{
		std::cout	<< "Calculating a difference (a - b).\n"
					<< "Please enter the first number: ";
		std::cin >> a;

		std::cout	<< "Please enter the second number: ";
		std::cin >> b;

		std::cout << "a - b equals " << (a - b);
	}
	else if (choice == 3)
	{
		std::cout	<< "Calculating a product (a * b).\n"
					<< "Please enter the first number: ";
		std::cin >> a;

		std::cout	<< "Please enter the second number: ";
		std::cin >> b;

		std::cout << "a * b equals " << (a * b);
	}
	else if (choice == 4)
	{
		std::cout	<< "Calculating a quotient (a / b).\n"
					<< "Please enter the first number: ";
		std::cin >> a;

		std::cout	<< "Please enter the second number: ";
		std::cin >> b;

		if (b == 0)
			std::cout << "Cannot divide by 0!";
		else
			std::cout << "a / b equals " << (a / b);
	}
	else
		std::cout << "Invalid option: " << choice;
}

Explaination

important

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1. Main menu

cout is used to print the main program menu at the very beginning (Lesson - 1. First program). We chained a multiple text printings using << operators.

2. Choice

To determine which math operation should be executed we use if, else if and else statements (Lesson - 4. Conditions)

Things to improve

1. Repeating code

You can easily spot a piece of code that is repeated several times:

⚠ Repeated code fragment

std::cout << "Please enter the first number: ";
std::cin >> a;

std::cout << "Please enter the second number: ";
std::cin >> b;

You'll learn how to solve this problem in the course, by using functions.

2. Detecting input failures

What would happen if you tried to enter a word (f.e.: hello) instead of a number in this part of the code:

🤔 Will it work?

int choice;
std::cin >> choice; // entering "hello"

TODO: lesson about input reading failures