In programming languages that include a distinct boolean data type in their type system, like Pascal, Ada, Python or Java, these operators usually evaluate to true or false, depending on if the conditional relationship between the two operands holds or not.
It is used in switch statements to dispatch the control flow to the correct branch, and during the unification process in logic programming.
Sometimes, particularly in object-oriented programming, the comparison raises questions of data types and inheritance, equality, and identity.
Real numbers, including many simple fractions, cannot be represented exactly in floating-point arithmetic, and it may be necessary to test for equality within a given tolerance.
Although such behaviour is typically meant to make the language easier, it can lead to surprising and difficult to predict consequences that many programmers are unaware of.
Greater than and less than comparison of non-numeric data is performed according to a sort convention (such as, for text strings, lexicographical order) which may be built into the programming language and/or configurable by a programmer.
When it is desired to associate a numeric value with the result of a comparison between two data items, say a and b, the usual convention is to assign −1 if a < b, 0 if a = b and 1 if a > b.
The following four conditional statements all have the same logical equivalence E (either all true or all false) for any given x and y values: This relies on the domain being well ordered.
For example, an expression in Python will print the message if the x is less than y: Other programming languages, such as Lisp, use prefix notation, as follows: In mathematics, it is common practice to chain relational operators, such as in 3 < x < y < 20 (meaning 3 < x and x < y and y < 20).
However, many recent programming languages would see an expression like 3 < x < y as consisting of two left (or right-) associative operators, interpreting it as something like (3 < x) < y.
It is possible to give the expression x < y < z its familiar mathematical meaning, and some programming languages such as Python and Raku do that.
The D programming language does not do that since it maintains some compatibility with C, and "Allowing C expressions but with subtly different semantics (albeit arguably in the right direction) would add more confusion than convenience".
and subsequently made it tempting to use the remaining = character for copying, despite the obvious incoherence with mathematical usage (X=X+1 should be impossible).
Its sole intended application was as a vehicle for a first port of (a then very primitive) Unix, but it also evolved into the very influential C language.
B started off as a syntactically changed variant of the systems programming language BCPL, a simplified (and typeless) version of CPL.
Some programmers get in the habit of writing comparisons against a constant in the reverse of the usual order: If = is used accidentally, the resulting code is invalid because 2 is not a variable.