C++ program to calculate area of the circle if the radius is greater than 0 using goto statement.

#include <iostream>
using namespace std;

// Function to calculate area of the circle using pass-by-value
void calculateAreaByValue(double radius) {
    double area = 3.14159 * radius * radius;
    cout << "Area of the circle (By Value): " << area << endl;
}

// Function to calculate area of the circle using pass-by-reference
void calculateAreaByReference(double &radius, double &area) {
    area = 3.14159 * radius * radius;
    cout << "Area of the circle (By Reference): " << area << endl;
}

int main() {
    double radius, area;

    // Label for the goto statement
    start:
    cout << "Enter the radius of the circle (must be greater than 0): ";
    cin >> radius;

    // Check if the radius is valid
    if (radius <= 0) {
        cout << "Invalid input! Radius must be greater than 0." << endl;
        goto start; // Go back to the start label to re-enter the value
    }

    // Calculate area using pass-by-value
    cout << "=== Pass-by-Value Calculation ===" << endl;
    calculateAreaByValue(radius);

    // Calculate area using pass-by-reference
    cout << "\n=== Pass-by-Reference Calculation ===" << endl;
    calculateAreaByReference(radius, area);
    cout << "Area after calculateAreaByReference: " << area << endl;

    return 0;
}

#include <iostream>

using namespace std;

// Function to calculate area of the circle using pass-by-value

void calculateAreaByValue(double radius) {

double area = 3.14159 * radius * radius;

cout << "Area of the circle (By Value): " << area << endl;

}

// Function to calculate area of the circle using pass-by-reference

void calculateAreaByReference(double &radius, double &area) {

area = 3.14159 * radius * radius;

cout << "Area of the circle (By Reference): " << area << endl;

}

int main() {

double radius, area;

// Label for the goto statement

start:

cout << "Enter the radius of the circle (must be greater than 0): ";

cin >> radius;

// Check if the radius is valid

if (radius <= 0) {

cout << "Invalid input! Radius must be greater than 0." << endl;

goto start; // Go back to the start label to re-enter the value

}

// Calculate area using pass-by-value

cout << "=== Pass-by-Value Calculation ===" << endl;

calculateAreaByValue(radius);

// Calculate area using pass-by-reference

cout << "\n=== Pass-by-Reference Calculation ===" << endl;

calculateAreaByReference(radius, area);

cout << "Area after calculateAreaByReference: " << area << endl;

return 0;

}

Explanation

1. Pass-by-Value (`calculateAreaByValue` Function)

Definition:

C++
void calculateAreaByValue(double radius)
1
void calculateAreaByValue(double radius)
- Parameters: Accepts the radius of the circle as a parameter by value.
- Operation:
  - The function calculates the area of the circle using the formula π * radius^2, where π is approximated as 3.14159.
  - Displays the calculated area.
- Effect:
  - The original value of radius remains unchanged after the function call.

2. Pass-by-Reference (`calculateAreaByReference` Function)

Definition:

C++
void calculateAreaByReference(double &radius)
1
void calculateAreaByReference(double &radius)
- Parameters: Accepts the radius of the circle as a parameter by reference.
- Operation:
  - The function calculates the area of the circle using the same formula as above.
  - Displays the calculated area.
- Effect:
  - The radius variable is passed by reference, so any modifications to radius within the function would affect the original variable. However, in this case, the radius is not modified inside the function.

3. Input Validation Using `goto`

Label: The start label marks the point where the program should return if invalid input is entered.
Condition: The program checks if the entered radius is greater than 0.
Flow: If the radius is not greater than 0, the program prints an error message and prompts the user to re-enter the radius by jumping back to the start label.

Sample Output:

Enter the radius of the circle (greater than 0): -5
The radius must be greater than 0. Please try again.
Enter the radius of the circle (greater than 0): 3
=== Pass-by-Value Calculation ===
Area of the circle (By Value): 28.2743

=== Pass-by-Reference Calculation ===
Area of the circle (By Reference): 28.2743

Enter the radius of the circle (greater than 0): -5

The radius must be greater than 0. Please try again.

Enter the radius of the circle (greater than 0): 3

=== Pass-by-Value Calculation ===

Area of the circle (By Value): 28.2743

=== Pass-by-Reference Calculation ===

Area of the circle (By Reference): 28.2743

Key Points

Area Calculation:
- The area of the circle is calculated using the formula π * radius^2.
- The program approximates π as 3.14159.
Pass-by-Value:
- The function receives a copy of the radius.
- The original variable is unaffected by changes made inside the function.
Pass-by-Reference:
- The function receives a reference to the radius.
- Any changes to radius inside the function would affect the original variable, though in this case, the radius is not modified.
Input Validation with goto:
- The goto statement is used to ensure the user enters a valid radius (greater than 0).
- The program prompts the user to re-enter the radius if the input is invalid.

Explanation

1. Pass-by-Value (calculateAreaByValue Function)

2. Pass-by-Reference (calculateAreaByReference Function)

3. Input Validation Using goto

Key Points

Related Posts:

1. Pass-by-Value (`calculateAreaByValue` Function)

2. Pass-by-Reference (`calculateAreaByReference` Function)

3. Input Validation Using `goto`