ifstatement

IfStatement is a control-flow construct used in many programming languages to perform conditional execution. It directs the program to take one path of code if a given boolean condition is true, and an alternative path if the condition is false. In some languages, the construct can chain multiple conditions with else-if or elseif clauses.

Structure and variants: A typical IfStatement includes a condition expression, a then-block to execute when the condition is true, and an optional else-block to execute when the condition is false. Many languages also support an else-if ladder to test additional conditions in sequence. Some languages provide a single-line form for compact conditions, while others require multiline blocks and braces or indentation.

Semantics: The condition is evaluated, and based on its truth value, the corresponding block is executed. Only one branch runs for a given evaluation. Conditions may involve side effects, and in languages with short-circuit boolean operators, the evaluation of a condition can affect program state even before the then- or else-block runs.

Examples: In C-like syntax, if (x > 0) { printf("%d\\n", x); } else { printf("non-positive\\n"); }. In Python, if x > 0: print(x) else: print("non-positive"). The concept also appears as an IfStatement in an abstract syntax tree (AST) used by compilers, with fields for the condition, the then-branch, and the else-branch.

Relation to other constructs: IfStatement contrasts with switch or case statements, which select among many branches, and with conditional expressions that yield a value without introducing a separate block. Potential pitfalls include reliance on truthiness rules and ensuring all execution paths are handled.