#include <iostream>
#include <string>

// Namespace for a graphics library
namespace GraphicsLib {
    struct Color {
        int r, g, b;
    };

    void draw(const std::string& shape, const Color& color) {
        std::cout << "GraphicsLib: Drawing a " << shape << " with color RGB("
                  << color.r << "," << color.g << "," << color.b << ")" << std::endl;
    }

    int getArea(int width, int height) {
        std::cout << "GraphicsLib: Calculating area of a rectangle" << std::endl;
        return width * height;
    }
}

// Namespace for a math library
namespace MathLib {
    struct Point {
        double x, y;
    };

    void draw(const Point& start, const Point& end) {
        std::cout << "MathLib: Drawing a line from (" << start.x << "," << start.y
                  << ") to (" << end.x << "," << end.y << ")" << std::endl;
    }

    double getArea(double radius) {
        std::cout << "MathLib: Calculating area of a circle" << std::endl;
        return 3.14159 * radius * radius;
    }
}

// A function in the global namespace
void draw() {
    std::cout << "Global: Drawing nothing in particular" << std::endl;
}

int main() {
    // Using fully qualified names
    GraphicsLib::Color red = {255, 0, 0};
    GraphicsLib::draw("square", red);

    MathLib::Point p1 = {0, 0}, p2 = {5, 5};
    MathLib::draw(p1, p2);

    // Calling the global draw function
    ::draw();

    // Using namespace directives (generally avoided in practice)
    using namespace GraphicsLib;
    using namespace MathLib;

    // This would cause an error due to ambiguity:
    // draw(/* parameters */);

    // Resolving the ambiguity
    GraphicsLib::draw("circle", {0, 255, 0});
    MathLib::draw({1, 1}, {4, 5});

    // Functions with the same name but different parameters
    std::cout << "Rectangle area: " << GraphicsLib::getArea(4, 5) << std::endl;
    std::cout << "Circle area: " << MathLib::getArea(3) << std::endl;

    // Using a namespace alias
    namespace GL = GraphicsLib;
    GL::Color blue = {0, 0, 255};
    GL::draw("triangle", blue);

    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
}