Variables, Expressions, and Types

Naming Values and Expressions

A variable is a named box holding a value your program can read and change. Assignment puts a value into a variable, written as x = 5, read as "let x become 5." Assignment is directional: the right side evaluates first, then stores into the left.

An expression is any combination of values, variables, and operators evaluating to a single value. Operator precedence dictates that multiplication binds tighter than addition, so $3 + 4 \times 2 = 11$. Parentheses override this: $(3 + 4) \times 2 = 14$.

Common pitfall: Never read x = x + 1 as a mathematical equation. It is a command: read current x, add 1, and store the result back into x.

Types and Operations

Every value has a type dictating what it holds and which operations are valid. Operations depend heavily on types, especially with overloaded operators like +.

Distinction: The + operator adds two integers ($1 + 1 = 2$), but it concatenates two strings ("1" + "1" = "11"). Mixing types carelessly causes subtle bugs.