Use relational operators

Relational operators compare two values or strings to provide a true or false result. The result of a relational operation is a BOOL value.
If the comparison is
The result is
True
1
False
0
Use these relational operators.
For this comparison
Use this operator
Optimal data type
Equal
=
DINT, REAL, String type
Less than
<
DINT, REAL, String type
Less than or equal
<=
DINT, REAL, String type
Greater than
>
DINT, REAL, String type
Greater than or equal
>=
DINT, REAL, String type
Not equal
<>
DINT, REAL, String type
The table provides examples of using relational operators
Use this format
Example
For this situation
Write
value1 operator value2
If temp is a DINT tag and your specification says: ‘If temp is less than 100⋅ then…’
IF temp<100 THEN...
stringtag1 operator stringtag2
If bar_code and dest are string tags and your specification says: ‘If bar_code equals dest then…’
IF bar_code=dest THEN...
stringtag1 operator 'character string literal'
If bar_code is a string tag and your specification says: ‘If bar_code equals ’Test PASSED’ then...’
IF bar_code=’Test PASSED’ THEN...
char1 operator char2
To enter an ASCII character directly into the expression, enter the decimal value of the character.
If bar_code is a string tag and your specification says: ‘If bar_code.DATA[0] equals ’A’ then…’
IF bar_code.DATA[0]=65 THEN...
bool_tag := bool_expressions
If count and length are DINT tags, done is a BOOL tag, and your specification says: ‘If count is greater than or equal to length, you are done counting.’
Done := (count >= length);
How strings are evaluated
The hexadecimal values of the ASCII characters determine if one string is less than or greater than another string.
  • When the two strings are sorted as in a telephone directory, the order of the strings determines which one is greater.
StringEvaluationGraphic
  • Strings are equal if their characters match.
  • Characters are case sensitive. Upper case "A" ($41) is not equal to lower case "a" ($61).
Provide Feedback
Have questions or feedback about this documentation? Please submit your feedback here.