# Introduction

In computer programming, we are giving instructions to the computer to process. The instructions we give can be made up of different idioms. We have already looked at a few of these, such as initializing variables with values, and creating functions. We will now consider an idiom known as an expression. Expressions are used to evaluate into either, true, false, or a numeric value.

# What is an Expression?

An expression has three parts:

1. Variable or Literal
2. Operator
3. Variable or Literal

For example:

``````a > 4
``````

In this example, we have the three components of an expression:

1. Variable or Literal: In this case, the variable 'a'.
2. Operator: In this case, the "greater than" operator.
3. Variable or Literal: In this case, the numeric literal '4'.

Here is another example:

``````b == c
``````

In this example, we have the three components of an expression:

1. Variable or Literal: In this case, the variable 'b'.
2. Operator: In this case, the "equivalence" operator.
3. Variable or Literal: In this case, the variable 'c'.

And here is a final example:

``````5 * 3
``````

In this example, we have an arithmetic expression. Here, the three components of an expression are:

1. Variable or Literal: In this case, the literal '5'.
2. Operator: In this case, the "equivalence" operator.
3. Variable or Literal: In this case, the literal '3'.

# Operators

Operators are used to compare or transform the terms on either side of it. The operators are categorized into Algebraic, Comparative and Boolean Algebraic.

## Algebraic Operators

• Subtraction: -
• Multiplication: *
• Division: /
• Modulus: %

Note: The modulus operator is very useful, yet often underutilized. For those unfamiliar with the modulus operation, it is used to return the remainder from a division. So, for example, 10 / 5 = 2 remainder 0, thus 10 % 5 is 0. If we look at 7 / 2 = 3 remainder 1, thus 7 % 2 is 1. Why is this useful? Well, for many reasons. One very useful situation is where you need to find out if a number is a factor of another number (this is referred to as a Factor). Another example for use is when you need to find even and odd numbers. So if you use x % 2, when this equates to 0, x is even, and when it equates to 1, x is odd.

## Comparison Operators

• Equivalence: ==
• Greater than: >
• Lesser than: <
• Inequality: !=
• Greater than or equal to: >=
• Lesser than or equal to: <=

• AND: and
• OR: or
• NOT: !
• XOR: ^

# Examples

Algebraic

``````1 + 2
b - 4
a * x
4 / 2
10 % 5
``````

Comparison

``````a > 10
c < 1
5 == x
8 != d
``````

Boolean Algebraic

``````1 and b
c or not d
1011 ^ 0101
``````

# Exercises

Which of the following are NOT expressions, and why?

1. x and y or z
2. a % 10
3. x = 1
4. f(x) = 2 * x

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