C++ · Functions and overloading

• A function must be declared before it is called. The declaration (prototype) and the definition can live in different places, which is how header files work.
• Default arguments work like Python’s, but go in the declaration.
• Overloading: several functions can share one name as long as their parameter types differ. The compiler picks the best match at compile time. Python has nothing built in like this.
• Lambdas: [capture](params) { body }. [=] captures by copy and [&] by reference.

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

double area(double r);                       // declaration (prototype)

int add(int a, int b)                { return a + b; }
double add(double a, double b)       { return a + b; }
std::string add(const std::string& a, const std::string& b) { return a + b; }

void greet(const std::string& name, const std::string& greeting = "Hello") {
    std::cout << greeting << ", " << name << "!\n";
}

int main() {
    std::cout << add(2, 3) << ' ' << add(2.5, 0.25) << ' ' << add(std::string("C+"), std::string("+")) << '\n';
    greet("Sahaj");
    greet("Sahaj", "Namaste");
    std::cout << area(1.0) << '\n';

    int bonus = 5;
    std::vector<int> marks{70, 85, 92};
    std::for_each(marks.begin(), marks.end(), [bonus](int& m) { m += bonus; });
    for (int m : marks) std::cout << m << ' ';
    std::cout << '\n';
}

double area(double r) { return 3.14159 * r * r; }   // definition later

Output:

5 2.75 C++
Hello, Sahaj!
Namaste, Sahaj!
3.14159
75 90 97