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CASE Statements

The CASE statement is used when a variable or expression can have multiple discrete values and you want to execute different logic depending on each value. It's similar to switch statements in other languages.

Syntax​

CASE <expression> OF
    <value1>: <statements>;
    <value2>: <statements>;
    ...
ELSE
    <default_statements>;
END_CASE;
  • <expression> must be a value like an DINT
  • Each <value> represents a possible match
  • ELSE is optional but recommended as a fallback
  • Always end with END_CASE;

Example: Mode Selector​

CASE Mode OF
    1: Operation := 'Auto';
    2: Operation := 'Manual';
    3: Operation := 'Maintenance';
ELSE
    Operation := 'Unknown';
END_CASE;

Example: Speed Level Control​

CASE Speed_Level OF
    0: Motor_Speed := 0;
    1: Motor_Speed := 25;
    2: Motor_Speed := 50;
    3: Motor_Speed := 100;
ELSE
    Motor_Speed := 0; // Default if out of range
END_CASE;

When to Use CASE Instead of IF​

Use CASE when:

  • You’re checking one variable against multiple values

  • You want better readability than multiple IF...ELSIF blocks

  • Your logic branches are simple and based on a single input

Notes​

  • CASE only checks for equality (=). It does not support relational operators (<, >, etc.)

  • For range checks or more complex logic, use IF...THEN...ELSE