Logical Operators in Programming

In the previous section, we looked at arithmetic operators. Another programming operator that may be familiar to you from maths topics are logical operators. These allow you to compare two values against each other and produce a boolean result (True or False).

Calculator maths

Logical operators are used in programs to make decisions in both selective and iterative statements. (For more information on these, see the programming constructs pages on selection and iteration)

Logical operators in programming include:

<less than
>more than
<=less than or equal to
>=more than or equal to
==equal to
!=not equal to (aka <>)

Selective statements like IF statements make use of logical operators to compare two values against each other, producing a boolean result. For example, if we wrote a program to check a password was correct, we would need to compare the string that the user entered agains the string saved for the correct password. In pseudocode this would look like:

password = "teachallaboutit"
OUTPUT "Please enter your password:"
userPassword = INPUT

IF password == userPassword THEN
OUTPUT "password accepted"
ELSE:
OUTPUT "password incorrect"

The code below implements this pseudocode in Python. click on the code & press Ctrl + Enter to run it.

Try adjusting the code so that the user is asked to enter the correct password repeatedly until it is correct.

Why these symbols?

The logical operators that we use are very similar to those used in maths, with the exceptions of the “or equal to” where maths uses a combined symbol of ≤ or ≥, and the not equal to symbol of  ≠.

The reason for the difference in these symbols is that programming source code is all written in plain text which uses the ASCII character set. So, because ASCII does not contain the mathematical symbols alternatives had to be found.

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