Variables and Data Types in Programming

Supporting explainer · Computer Science · 1 min read

What variables and common data types are, with short Python examples.

In programming, a variable is a named place that stores a value. The value can change as the program runs.

Creating variables (Python)

age = 15
price = 4.99
name = "Sam"
is_student = True

Common data types

Operations depend on type

• 5 + 3 gives 8 (integer addition).
• "5" + "3" gives "53" (strings are joined).
• "5" + 3 causes an error in Python because the types do not match. Convert first: int("5") + 3 gives 8.

Integer and decimal division in Python

• 7 / 2 gives 3.5.
• 7 // 2 gives 3 (whole-number division).
• 7 % 2 gives 1 (remainder).

Naming

Use clear names, such as total_score, not x. In Python, names cannot start with a digit or contain spaces.

Assignment is not equality

In x = x + 1, the = means "store the result on the right in the variable on the left", not "x equals x plus one". After it runs, x is one larger.

Common mistakes

• Mixing types without converting.
• Misspelling a variable name, which creates a new one or an error.
• Treating = as a mathematical equals sign. To compare, use ==.

Quick recap

Variables store values. Each value has a type that determines what operations are allowed. Convert types when needed.