C++ do-while Loop Solutions and Examples

Explore solved C++ do-while loop exercises, including a menu-driven calculator, algorithm analysis, dry runs, complete code, and sample output.

Contents

• LOOP-COD-019: Simple Calculator Menu

Solution: LOOP-COD-019 - Simple Calculator Menu

1. Problem Analysis

The task is to develop a menu-driven calculator using a do-while loop.

The program should repeatedly display a menu and allow the user to perform addition or subtraction until the user selects Exit.

Input:

• User’s menu choice (1, 2, or 3).
• Two numbers for addition or subtraction.

Processing:

• If the choice is 1, add the two numbers.
• If the choice is 2, subtract the second number from the first.
• If the choice is 3, terminate the loop.
• For any other choice, display an error message.

Output:

• Sum of two numbers.
• Difference between two numbers.
• Error message for an invalid choice.
• Calculator closed. when the user exits.

Programming concepts required:

• do-while loop
• switch statement
• Variables
• User input and output
• Arithmetic operators

2. Algorithm / Pseudocode

1. Start the program.
2. Declare variables for the menu choice and two numbers.
3. Display the calculator menu.
4. Ask the user to enter a choice.
5. Check the user’s choice:
   • If choice is 1:
     • Ask for two numbers.
     • Calculate their sum.
     • Display the sum.
   • If choice is 2:
     • Ask for two numbers.
     • Calculate their difference.
     • Display the difference.
   • If choice is 3:
     • Display Calculator closed.
   • Otherwise:
     • Display an invalid choice message.
6. Repeat the menu while the choice is not 3.
7. End the program.

Pseudocode

START

DO
    DISPLAY calculator menu
    INPUT choice

    SWITCH choice
        CASE 1:
            INPUT num1, num2
            sum = num1 + num2
            DISPLAY sum
            BREAK

        CASE 2:
            INPUT num1, num2
            difference = num1 - num2
            DISPLAY difference
            BREAK

        CASE 3:
            DISPLAY "Calculator closed."
            BREAK

        DEFAULT:
            DISPLAY "Invalid choice."

WHILE choice is not equal to 3

STOP

3. Dry Run Table

A dry run helps us understand how the program executes with the given sample input.

Given input:

1
10 5
2
10 5
3

Understanding the loop:

• First iteration: The user selects Addition. The program calculates 10 + 5 = 15.
• Second iteration: The user selects Subtraction. The program calculates 10 - 5 = 5.
• Third iteration: The user selects Exit. The program displays the closing message.
• The loop terminates because the choice is 3.

4. Complete C++ Code

#include <iostream>
using namespace std;

int main()
{
    int choice;
    float num1, num2;

    do
    {
        cout << "\n===== Simple Calculator =====" << endl;
        cout << "1. Addition" << endl;
        cout << "2. Subtraction" << endl;
        cout << "3. Exit" << endl;

        cout << "Enter your choice: ";
        cin >> choice;

        switch (choice)
        {
            case 1:
                cout << "Enter two numbers: ";
                cin >> num1 >> num2;

                cout << "Sum = " << num1 + num2 << endl;
                break;

            case 2:
                cout << "Enter two numbers: ";
                cin >> num1 >> num2;

                cout << "Difference = " << num1 - num2 << endl;
                break;

            case 3:
                cout << "Calculator closed." << endl;
                break;

            default:
                cout << "Invalid choice! Please try again." << endl;
        }

    } while (choice != 3);

    return 0;
}

5. Code Explanation

Let’s understand the important parts of the program.

A. Declare variables

int choice;
float num1, num2;

• choice stores the menu option entered by the user.
• num1 stores the first number.
• num2 stores the second number.
• float allows the calculator to work with decimal numbers.

B. The do-while loop

do
{
    // Menu and calculator operations

} while (choice != 3);

A do-while loop executes its body at least once before checking the condition.

Here, choice != 3 means the loop continues as long as the user does not select Exit.

When the user enters 3, the condition becomes false, and the loop terminates.

C. Display the menu

cout << "\n===== Simple Calculator =====" << endl;
cout << "1. Addition" << endl;
cout << "2. Subtraction" << endl;
cout << "3. Exit" << endl;

These statements display the calculator menu each time the loop executes.

D. Get the user’s choice

cout << "Enter your choice: ";
cin >> choice;

The program asks the user to select an option and stores it in the choice variable.

E. Use the switch statement

switch (choice)

The switch statement checks the selected menu option and executes the matching case.

• case 1: Performs addition.
• case 2: Performs subtraction.
• case 3: Displays the closing message.
• default: Handles invalid choices.

F. Perform addition

cin >> num1 >> num2;
cout << "Sum = " << num1 + num2 << endl;

The program takes two numbers and adds them using the + operator.

G. Perform subtraction

cin >> num1 >> num2;
cout << "Difference = " << num1 - num2 << endl;

The program subtracts the second number from the first using the - operator.

H. Understand the break statement

break;

The break statement terminates the current switch case. It does not terminate the do-while loop.

The loop continues until the user selects 3.

6. Sample Output

===== Simple Calculator =====
1. Addition
2. Subtraction
3. Exit
Enter your choice: 1
Enter two numbers: 10 5
Sum = 15

===== Simple Calculator =====
1. Addition
2. Subtraction
3. Exit
Enter your choice: 2
Enter two numbers: 10 5
Difference = 5

===== Simple Calculator =====
1. Addition
2. Subtraction
3. Exit
Enter your choice: 3
Calculator closed.

7. Modification Task

Now modify the existing calculator program to practise independently.

Task 1: Add Multiplication

• Add a new menu option: 3. Multiplication.
• If the user selects 3, ask for two numbers.
• Multiply the numbers and display the result.

Task 2: Update the Exit Option

• Change the Exit option from 3 to 4.
• Update the loop condition accordingly.
• Display Calculator closed. when the user selects 4.

Task 3: Add Division

• Add a new menu option: 4. Division.
• Ask for two numbers.
• Display their division result.
• Check whether the second number is zero before performing division.

Challenge: Update the menu and program so that all four arithmetic operations work correctly, and the user can continue calculating until selecting Exit.

Key Learning Point: The do-while loop is useful for menu-driven programs because it displays the menu at least once and repeats it until the user chooses to exit.