Variables, Types, and Expressions

Storing Values and Types

A program computes by manipulating values held in variables. A variable is a named container where assignment stores a value, and using its name retrieves it.

Assignment is a command, not a math equation. Writing x = x + 1 means compute x + 1 and store the result back into x, updating the variable.

Every value has a data type dictating valid operations. The symbol + adds numbers but concatenates strings.

Expressions and Pitfalls

Expressions combine values and variables with operators. They follow precedence rules where multiplication happens before addition, overridden by parentheses.

For example, $2 + 3 \times 4$ evaluates to 14, because the operator * binds tighter than +.

Floating-point numbers use finite precision and are approximate. Due to rounding, $0.1 + 0.2$ does not exactly equal $0.3$.