CASE Statements

CASE checks one numeric expression and runs the statements that match the first selector. It keeps branching tidy compared to a long IF...ELSIF chain.

Syntax

CASE numeric_expression OF
    selector1: Statements;
    selector2: Statements;
    selector3, selector4: Statements; // Matches selector3 or selector4
    selector5..selector6: Statements; // Matches any value from selector5 to selector6
ELSE
    Default_Statements;
END_CASE;

Syntax Rules

• numeric_expression can be any DINT or REAL tag or math expression.
• Each selector is a literal value (for example 1 or 7.5). You cannot use tag names as selectors.
• Separate multiple selectors with commas (,).
• Use two dots (..) for an inclusive range such as 0..10.
• ELSE is optional but helpful as a default branch.
• Always finish the block with END_CASE;.
• With REAL selectors, ranges work better than matching a single decimal value.

Example: Mode Selector

CASE Mode OF
    1: Operation_Code := 10;
    2: Operation_Code := 20;
    3: Operation_Code := 30;
ELSE
    Operation_Code := 0; // Default
END_CASE;

This sets Operation_Code based on the current Mode value. If Mode is not 1, 2, or 3, the ELSE branch executes.

Example: Speed Level Control with Ranges

CASE Speed_Level OF
    0: Motor_Speed := 0;
    1..3: Motor_Speed := 25; // Values 1, 2, 3
    4..6: Motor_Speed := 50;
    7..10: Motor_Speed := 100;
ELSE
    Motor_Speed := 0; // Fallback if out of range
END_CASE;

This example uses numeric ranges to group related values. Each range is inclusive of both start and end values.

Example: Multiple Selectors (Comma-Separated)

CASE Error_Code OF
    1, 2, 3: Reset_Flag := 1; // Matches any of 1, 2, or 3
    4, 5: Reset_Flag := 0;
ELSE
    Reset_Flag := 0;
END_CASE;

Comma-separated selectors allow multiple exact values to share the same action.

When to Use CASE Instead of IF

• Comparing one numeric expression to several values
• You want cleaner logic than stacked IF...ELSIF
• You need to group ranges or sets of numbers under one result

Notes

• Use IF...THEN...ELSE when conditions depend on multiple variables or relational comparisons.
• END_CASE; still needs the semicolon.
• Include an ELSE section when you need a defined default outcome.

Summary Table