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.
- Strings are equal if their characters match.
- Characters are case sensitive. Upper case "A" ($41) is not equal to lower case "a" ($61).
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