If Then

The conditional is one of two primary programming constructs (the other being the loop) that is present in almost every programming language. After all, even in those rare cases where the computer is just repeatedly adding values or doing some other repetitive activity, at some point a decision is needed and a condition evaluated, even if the question is only "is it time to stop?" Visual Basic supports the If- Then statement as well as the Else statement; — and unlike some languages, the concept of an Elself statement. The ElseIf and Else statements are totally optional, and it is not only acceptable but common to use conditionals that do not utilize either of these code blocks. The following example illustrates a simple pair of conditions that have been set up serially:


'Code C3 End If

If the first condition is true, then code placed at marker A1 is executed. The flow would then proceed to the End If, and the program would not evaluate any of the other conditions. Note that for best performance, it makes the most sense to have your most common condition first in this structure, because if it is successful, none of the other conditions need to be tested.

If the initial comparison in the preceding example code were false, then control would move to the first Else statement, which in this case happens to be an ElseIf statement. The code would therefore test the next conditional to determine whether the value of i were less than 1. If so, then the code associated with block B2 would be executed.

However, if the second condition were also false, then the code would proceed to the Else statement, which isn't concerned with any remaining condition and just executes the code in block C3. Not only is the Else optional, but even if an ElseIf is used, the Else condition is still optional. It is acceptable for the Else and C3 block to be omitted from the preceding example.

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