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;