C++ functions let you package a task into a reusable block of code. Instead of repeating the same math or logic throughout a program, you can give that operation a name, pass information into it through parameters, and return a result.

A simple function

int add(int a, int b) {
    return a + b;
}

Here, int is the return type, add is the function name, and a and b are parameters. The return statement sends the calculated value back to the code that called the function.

Calling the function

#include <iostream>

int add(int a, int b) {
    return a + b;
}

int main() {
    int total = add(12, 8);
    std::cout << total << '\n';
    return 0;
}

The values 12 and 8 are arguments. When the function runs, those arguments initialize the parameters a and b. The function returns 20, which is stored in total.

Parameters versus arguments

A parameter is the variable named in a function declaration or definition. An argument is the value or expression supplied when the function is called. Keeping those terms separate makes larger programs easier to discuss and debug.

A practical electrical example

#include <iostream>

double power_kw(double volts, double amps) {
    return (volts * amps) / 1000.0;
}

int main() {
    double kw = power_kw(240.0, 20.0);
    std::cout << kw << " kW\n";
    return 0;
}

This function accepts voltage and current as parameters and returns calculated power in kilowatts. With 240 volts and 20 amps, the result is 4.8 kW for this simple DC or unity-power-factor example. Real AC power calculations may also require power factor and phase considerations.

Functions that return nothing

void show_status() {
    std::cout << "System online\n";
}

The void return type means the function does not return a value to its caller. It can still perform work such as printing information or updating program state.

Why functions matter

Functions make programs easier to organize, test, reuse, and troubleshoot. A larger application can separate calculations, hardware checks, user-interface behavior, networking, and other jobs into clearly named functions rather than placing everything inside main().

Quick practice

Create a function named watts that accepts voltage and current and returns watts. Then create another function named is_over_limit that accepts a measured value and a limit and returns a Boolean result.

References

For deeper study, see the C++ function documentation at cppreference and Microsoft Learn.

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