3. Functions

Scope

Variables declared inside of blocks are called local variables

they are only accessible inside of that block

int a = 0;
if(a < 10)
{
  // Variable 'b' is only accessible inside of this 'if' block
  int b = 1;
  b = 2;          // This works
}
b = 3;              // This throws an error

Introduction to functions

To avoid repetition, blocks of code can be enclosed into named functions
Functions can have multiple arguments and a return type
```
void PrintName(string argument1)
{
    Debug.Log("My name is " + argument1);
}
```
- This function takes in one string argument
- It returns nothing (thus, its return type is void)
- The function can be called like this:
```
PrintName("Matti");
string name2 = "Teppo";
PrintName(name2);
```

Function example

Here’s an example with two arguments and a non-void return value

The return keyword tells what we return from the function

float Pythagoras(float a, float b) // a^2 + b^2 = c^2
{
    float c = Mathf.Sqrt(Mathf.Pow(a,2) + Mathf.Pow(b,2));
    return c;
}

The function is called like this:

float length = Pythagoras(3f, 4f); // now value of length is 5

The function definition can be further simplified…

float Pythagoras(float a, float b) // a^2 + b^2 = c^2
{
    return Mathf.Sqrt(Mathf.Pow(a,2) + Mathf.Pow(b,2));
}

Note about functions

Because C# is object-oriented, all functions are methods inside classes
We’ll dive deeper into these topics in Chapter 6. Classes and Methods

Setter methods

A common type of method in C# is a setter
Named something like SetVariableName

Takes in a new value for the variable

void SetName(string newName)
{
    name = newName;
}

If we change variable value with a setter method like this, we can easily track the changes by adding a Debug.Log call inside the method.

Exercise 1: Traffic lights

Create a script for displaying the state of a traffic light in the Unity console. We do it by creating a function called SetColor that takes in the color as a string argument.

⭐ Display the current color in the console every frame (use Update()).
For seconds 0-3 the color should be red, the seconds 4-5 should be yellow, and from that onwards green.
So, after the first frame the console would read The color is RED!.
Hint: Use Time.time to check the current time!

Exercise 1 extras

⭐⭐ Print the color to console only when the light changes.
⭐⭐⭐ Create a 3d object. Change the color of its material as a function of time.
- Spoiler:
```
gameObject.GetComponent<Renderer>().material.color = Color.green;
```

Programming 3. Functions