Semantic Analysis Quick Reference

Symbol Table Operations

• •INSERT(name, attributes): Add new symbol to current scope.
• •LOOKUP(name): Search current scope → enclosing scopes → global. Return attributes or error.
• •ENTER_SCOPE(): Push new scope (e.g., {, function body).
• •EXIT_SCOPE(): Pop current scope (e.g., }, end of function).
• •DELETE(name): Remove from current scope only (used for local declarations).

Type Checking Rules

// E1 + E2: both must be arithmetic; result = wider type
// E1 < E2: both must be comparable; result = bool
// E1 = E2: E2 must be assignable to type of E1
// &E: result = pointer to type of E
// *E: E must be pointer; result = pointed-to type
// f(args): arg types must match parameter types
// if (E): E must be bool (or implicitly convertible)

Scope Resolution (C Rules)

• •Block scope: Variables declared inside {} visible until end of block.
• •Function scope: Labels (goto targets) visible throughout function body.
• •File scope: Global variables and functions visible from declaration to end of file.
• •Shadowing: Inner scope re-declaration hides outer. No access to outer binding in C.
• •Forward declaration: extern or function prototype tells compiler the type exists.

Type Compatibility Matrix

Common Semantic Errors

• •Undeclared identifier: Variable used before declaration. Check scope, typo, or missing #include.
• •Type mismatch: Arithmetic on incompatible types (e.g., struct + int).
• •Redeclaration: Same name declared twice in same scope. C allows redeclaration in some contexts.
• •Void in expression: Using void value where value expected.
• •Break outside loop: break or continue outside for/while/switch.
• •Return type mismatch: Function returns value of wrong type or return; in non-void function.
• •Const violation: Assigning to const variable or through pointer-to-const.