Functions

Name a piece of work

A function packages a calculation under a name, so you can run it again with different inputs. You've already written one: main. Here's another:

double area(double width, double height) {
    return width * height;
}

int main() {
    std::cout << area(2, 3) << "\n";     // 6
    std::cout << area(0.5, 4) << "\n";   // 2
}

• The first double is the return type: the type of value the function gives back.
• Then come its name and its parameters in parentheses, each with its own type.
• The body goes between the braces. return hands a value back to whoever called the function: area(2, 3) runs the body with width = 2 and height = 3, and the whole call becomes 6.

Defining a function doesn't run it; calling it does. A function must be defined (or at least declared) above the code that calls it, so helper functions go above main.

A function that gives nothing back has the return type void:

void report(double x) {
    std::cout << "x = " << x << "\n";
}

return versus printing

Printing shows a value to you. return gives it back to the program, which can store it or use it in more maths: double total = area(2, 3) + area(1, 1);. The grader calls your functions and checks what they return, so always return the answer.

Every robot lesson is built this way: you'll write functions like forward_kinematics(q) that turn joint angles into a position.

Your task

1. Write deg_to_rad(deg) so it returns deg converted to radians.
2. Write reach(l1, l2) so it returns the reach of a two-link arm: the two lengths added together.

main calls both so you can see what they return. The grader tries each one on several inputs.