Conditionals and Boolean Logic

Making Decisions

Programs make decisions using conditional statements. An if statement runs code only when a condition is true; an if/else chooses between two paths; else if chains mutually exclusive cases. The condition is a boolean expression, evaluating to true or false.

Conditions rely on comparison operators to produce booleans:

Pitfall: Never confuse = (assignment: store a value) with == (comparison: test equality). Writing if (x = 5) assigns 5 instead of testing it.

Boolean Logic

Booleans combine using logical operators, matching propositional logic:

Operator precedence and parentheses control evaluation order. For safety, use parentheses: (x > 0) and (x < 10).

Languages use short-circuit evaluation: in $A \text{ and } B$, if $A$ is false, $B$ is skipped. This prevents runtime errors, allowing safe guards like checking if a list has items before inspecting its contents.