4. Loops

Loops?

• used for:
  • repeating blocks of code
  • looping through collections of data (more later...)
  • running a program (more laterer...)
• types of loops:
  • While
  • Do While
  • For
  • Foreach

while loop

• while loop keeps executing its code block as long as the condition in its statement is true:
  *

  int count = 0;
  while(count < 4)
  {
      Debug.Log(count);
      count++;
  }
  
  // Outputs '0', '1', '2' and '3'
  

do while loop

• similar to while loop, but it executes the code block once even if the statement isn't true
• try the following code: what happens if you change the initial value of count to 5?

int count = 0;
do
{
    Debug.Log(count);
    count++;
} while (count < 4);

// Outputs '0', '1', '2' and '3'

for loop

• for loops are used when the number of iterations is predefined
• for loop is initialized in three steps:

for (initialvalue;condition;increment)
{
    doStuff();
}

• The initial value is set before the first iteration
• The condition is checked before each iteration
• The increment is executed after each iteration

For loop example 1

for (int i = 0; i < 4; i++)
{
    Debug.Log("Current: " + i);
}
/* Outputs
Current: 0
Current: 1
Current: 2
Current: 3 
*/

For loop example 2

for (int i = 4; i > 0; i--)
{
    Debug.Log("Current: " + i);
}
/* Outputs
Current: 4
Current: 3
Current: 2
Current: 1 
*/

Breaking out of loops: break

• To stop the execution of a loop completely, use the break keyword:

  int i = 0;
  while (true)
  {
      i++;
      if (i == 3)
          break;
  }
  // i is now 3
  

Skip ahead: continue

• To skip the current iteration, use the continue keyword

  int i = 0;
  while(i < 10)
  {
      i++;
      if (i % 2 == 0)
          continue;
      Debug.Log(i);
  }
  // Prints every odd number from 1 to 10
  

Nested loops

• Loop inside a loop is often used for generating or going through two-dimensional data

  int rows = 3;
  int columns = 4;
  
  for (int i = 0; i < rows; i++)
  {
      for (int j = 0; j < columns; j++)
      {
          Debug.Log("(" + j.ToString() + "," + i.ToString() + ")");
      }
  }
  

  

While vs. for: when to use?

• for loops when the number of iterations is predefined
  • when going through a list, for example.
• while loops when we want to do something many times, but don't know when to stop

Exercise 1. Loops 1

Create a loop whose number of iterations is set in an integer variable numberOfEnemies.

Run a loop that many times and write the message Creating enemy 1, Creating enemy 2, etc. to console.

Exercise 2. Loops 2

Suppose you have a given number of collectibles in a level.

You want a given percentage of them, say, 10%, to be shiny collectibles.

Create a loop that runs until this condition is met, and prints into console Converted collectible 1 to shiny.

Exercise 3. Field of Cubes

Create a loop that instantiates a 8 * 8 field of cubes on a plane.

Extra: If there's a cube already in the location, add an exception to NOT add a cube there!