Program Flow Logic
- 30 Jan 2024
- Print
- PDF
Program Flow Logic
- Updated on 30 Jan 2024
- Print
- PDF
Article summary
Did you find this summary helpful?
Thank you for your feedback
Allows conditional execution, based on the evaluation of an expression.
Syntax 1: If condition Then thenpart [ Else elsepart]
Syntax 1 Remarks: The single-line form is often useful for short, simple conditional tests. Syntax 1 has these parts:
Part | Description |
|---|---|
If | Begins the simple If...Then control structure. |
Condition | One of two types of expressions: A numeric or string expression that evaluates true (nonzero) or false (0 and Null) . |
Then | Identifies actions to be taken if condition is satisfied. |
Thenpart | Statements or branches performed when condition is true |
Else | Identifies actions taken if condition is not satisfied. If the Else clause is not present, control passes to the next statement in the program. |
Elsepart | Statements or branches performed when condition is false |
Syntax 2
If condition1 Then [ statementblock-1]
[ ElseIf condition2 Then [ statementblock-2] ]
[ Else [ statementblock-n] ]
End If
Syntax 2 Remarks: The block form of If...Then...Else provides more structure and flexibility than the single-line form and is usually easier to read, maintain, and debug. Syntax 2 has these parts:
Part | Description |
|---|---|
If | Keyword that begins the block If...Then decision control structure. |
Condition1 | Same as condition used in the single-line form shown above. |
Then | Keyword used to identify the actions to be taken if a condition is satisfied. |
Statementblock-1 | One or more Visual Basic statements executed if condition1 is true |
ElseIf | Keyword indicating that alternative conditions must be evaluated if condition1 is not satisfied. |
Condition2 | Same as condition used in the single-line form shown above. |
Statementblock-2 | One or more Visual Basic statements executed if condition2 is true |
Else | Keyword used to identify the actions taken if none of the previous conditions are satisfied. |
Statementblock-n | One or more Visual Basic statements executed if condition1 and condition2 are both false. |
End If | Keyword that ends the block form of the If...Then. |
In executing a block If, Visual Basic tests condition1: the first numeric expression. If the expression is true, the statements following Then are executed.
If the first expression is, Visual Basic begins evaluating each ElseIf condition in turn. When Visual Basic finds a true condition, the statements immediately following the associated Then are executed. If none of the ElseIf conditions is true, the statements following the Else are executed. After executing the statements following Then or Else, the program continues with the statement following End If.
The Else and ElseIf clauses are both optional. There is no limit to the number of ElseIf clauses in a block If, but none can appear after an Else clause. Any of the statement blocks can contain nested block If statements. The block If must end with an End If statement.
Example: This example calculates the ratio of two input tags, depending on which is larger. If they are equal, the ELSE statement is executed.
If GD(1) > GD(2) Then
Result = GD(2)/GD(1)
ElseIf GD(2) > GD(1) Then
Result = GD(1)/GD(2)
Else
Result = 1
End If
Was this article helpful?