The if statement has various forms. The most basic form checks for a condition and will perform a subsequent block of code if, and only if, that condition is true. Consider the following code sample 1-2:

01 using UnityEngine;
02 using System.Collections;
03 
04 public class MyScriptFile : MonoBehaviour 
05 {
06     public string PlayerName = "";
07     public int PlayerHealth = 100;
08     public Vector3 Position = Vector3.zero;
09 
10     // Use this for initialization
11     void Start () {
12     }
13 
14     // Update is called once per frame
15     void Update () 
16     {
17         //Check player health - the braces symbol {} are option for one-line if-statements
18         if(PlayerHealth == 100)
19         {
20         Debug.Log ("Player has full health");
21         }
22     }
23 }

The preceding code is executed like all other types of code in Unity, by pressing the Play button from the toolbar, as long as the script file has previously been instantiated on an object in the active scene. The if statement at line 18 continually checks the PlayerHealth class variable for its current value. If the PlayerHealth variable is exactly equal to (==) 100, then the code inside the {} braces (in lines 19–21) will be executed. This works because all conditional checks result in a Boolean value of either true or false; the conditional statement is really checked to see whether the queried condition (PlayerHealth == 100) is true. The code inside the braces can, in theory, span across multiple lines and expressions. However, here, there is just a single line in line 20: the Debug.Log Unity function outputs the Player has full health string to the console, as shown in the following screenshot. Of course, the if statement could potentially have gone the other way, that is, if PlayerHealth was not equal to 100 (perhaps, it was 99 or 101), then no message would be printed. Its execution always depends on the previous if statement evaluating to true.

The Unity Console is useful for printing and viewing debug messages

More information on the if statements, the if-else statement, and their usage in C# can be found online at http://msdn.microsoft.com/en-GB/library/5011f09h.aspx.

You can, of course, check for more conditions than just equality (==), as we did in code sample 1-2. You can use the > and < operators to check whether a variable is greater than or less than another value, respectively. You can also use the != operator to check whether a variable is not equal to another value. Further, you can even combine multiple conditional checks into the same if statement using the && (AND) operator and the || (OR) operator. For example, check out the following if statement. It performs the code block between the {} braces only if the PlayerHealth variable is between 0 and 100 and is not equal to 50, as shown here:

if(PlayerHealth >= 0 && PlayerHealth <= 100 && PlayerHealth !=50)
{
Debug.Log ("Player has full health");
}

if(MyCondition)
{
//X - perform my code if MyCondition is true
}
else
{
//Y – perform my code if MyCondition is false
}

As we've seen, the if statement is useful to determine whether a single and specific condition is true or false and to perform a specific code block on the basis of this. The switch statement, in contrast, lets you check a variable for multiple possible conditions or states, and then lets you branch the program in one of many possible directions, not just one or two as is the case with if statements. For example, if you're creating an enemy character that can be in one of the many possible states of action (CHASE, FLEE, FIGHT, HIDE, and so on), you'll probably need to branch your code appropriately to handle each state specifically. The break keyword is used to exit from a state returning to the end of the switch statement. The following code sample 1-3 handles a sample enemy using enumerations:

01 using UnityEngine;
02 using System.Collections;
03 
04 public class MyScriptFile : MonoBehaviour 
05 {
06     //Define possible states for enemy using an enum
07     public enum EnemyState {CHASE, FLEE, FIGHT, HIDE};
08 
09     //The current state of enemy
10     public EnemyState ActiveState = EnemyState.CHASE;
11 
12     // Use this for initialization
13     void Start () {
14     }
15 
16     // Update is called once per frame
17     void Update () 
18     {
19          //Check the ActiveState variable
20          switch(ActiveState)
21          {
22          case EnemyState.FIGHT:
23          {
24                //Perform fight code here
25                Debug.Log ("Entered fight state");
26          }
27                break;
28 
29 
30          case EnemyState.FLEE:
31          case EnemyState.HIDE:
32          {
33               //Flee and hide performs the same behaviour
34               Debug.Log ("Entered flee or hide state");
35          }
36               break;
37 
38          default:
39          {
40               //Default case when all other states fail
41               //This is used for the chase state
42               Debug.Log ("Entered chase state");
43           }
44               break;
45           }
46     }
47 }

Another great benefit of enums is that variables based on them have their values appear as selectable options from drop-down boxes in the Object Inspector, as shown in the following screenshot:

Enumerations offer you drop-down options for your variables from the Object Inspector

More information on enums and their usage in C# can be found online at http://msdn.microsoft.com/en-us/library/sbbt4032.aspx.

The following are the comments for code sample 1-3: