#include <iostream>

// Abstract base class
class Shape {
public:
    // Pure virtual function
    virtual double area() const = 0;
    
    // Regular virtual function
    virtual void display() const {
        std::cout << "This is a shape." << std::endl;
    }
    
    virtual ~Shape() {
        std::cout << "Shape destructor called" << std::endl;
    }
};

class Circle : public Shape {
private:
    double radius;

public:
    Circle(double r) : radius(r) {}

    // Implementation of the pure virtual function
    double area() const override {
        return 3.14159 * radius * radius;
    }

    void display() const override {
        std::cout << "This is a circle with radius " << radius << std::endl;
    }

    ~Circle() override {
        std::cout << "Circle destructor called" << std::endl;
    }
};

class Rectangle : public Shape {
private:
    double width;
    double height;

public:
    Rectangle(double w, double h) : width(w), height(h) {}

    // Implementation of the pure virtual function
    double area() const override {
        return width * height;
    }

    void display() const override {
        std::cout << "This is a rectangle with width " << width << " and height " << height << std::endl;
    }

    ~Rectangle() override {
        std::cout << "Rectangle destructor called" << std::endl;
    }
};

int main() {
    // Shape shape;  // This would cause a compile error


    Shape* shape = new Shape();

    Shape* circle = new Circle(5);
    Shape* rectangle = new Rectangle(4, 6);

    std::cout << "Circle area: " << circle->area() << std::endl;
    circle->display();

    std::cout << "Rectangle area: " << rectangle->area() << std::endl;
    rectangle->display();

    delete circle;
    delete rectangle;

    return 0;
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

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

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}