Using If, Lbl, and Goto to Control Program Flow

The If command and several If...EndIf structures let you execute a statement or block of statements conditionally, that is, based on the result of a test (such as x>5). Lbl (label) and Goto commands let you branch, or jump, from one place to another in a function or program.

The If command and several If...EndIf structures reside on the Program Editor’s Control menu.

When you insert a structure such as If...Then...EndIf, a template is inserted at the cursor location. The cursor is positioned so that you can enter a conditional test.

If Command

To execute a single command when a conditional test is true, use the general form:

In this example, you must store a value to x before executing the If command.

If...Then...EndIf Structures

To execute one group of commands if a conditional test is true, use the structure:

Note: EndIf marks the end of the Then block that is executed if the condition is true.

If...Then...Else...EndIf Structures

To execute one group of commands if a conditional test is true and a different group if the condition is false, use this structure:

If...Then...ElseIf... EndIf Structures

A more complex form of the If command lets you test for multiple conditions. Suppose you want a program to test a user-supplied argument that signifies one of four options.

To test for each option (If Choice=1, If Choice=2, and so on), use the If...Then...ElseIf...EndIf structure.

Lbl and Goto Commands

You can also control the flow by using Lbl (label) and Goto commands. These commands reside on the Program Editor’s Transfers menu.

Use the Lbl command to label (assign a name to) a particular location in the function or program.

You can then use the Goto command at any point in the function or program to branch to the location that corresponds to the specified label.

Because a Goto command is unconditional (it always branches to the specified label), it is often used with an If command so that you can specify a conditional test. For example: