Type checking rules in Compiler Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Static Type Checking

Which of the following best describes static type checking in programming languages?

A Type errors are detected before the program runs, during compilation.

B Type errors are detected during program execution.

C Type checking is skipped entirely to improve performance.

D Type errors are fixed automatically by the compiler without reporting.

💡 Hint

Think about when the program is analyzed for type errors before running.

Static type checking means the compiler checks types before running the program, catching errors early.

📋 Factual

intermediate

Type Compatibility in Assignments

In type checking rules, when is an assignment between two variables considered valid?

A When the source type is a primitive and the target is a complex type.

B When the source and target types are completely unrelated.

C When the target type is a subtype of the source type only.

D When the source type can be implicitly converted to the target type.

💡 Hint

Consider if the language allows automatic conversion between types.

Assignments are valid if the source type can be implicitly converted to the target type, ensuring compatibility.

🔍 Analysis

advanced

Detecting Type Errors in Expressions

Given the expression a + b, which condition will cause a type error during type checking?

A <code>a</code> is a string and <code>b</code> is an integer, with no implicit conversion.

B Both <code>a</code> and <code>b</code> are integers.

C Both <code>a</code> and <code>b</code> are floats.

D <code>a</code> and <code>b</code> are both strings.

💡 Hint

Think about whether the language allows adding a string and an integer directly.

If there is no implicit conversion between string and integer, adding them causes a type error.

❓ Comparison

advanced

Static vs Dynamic Type Checking

Which statement correctly compares static and dynamic type checking?

A Static type checking allows more runtime flexibility than dynamic type checking.

B Static type checking finds errors at runtime; dynamic type checking finds errors at compile time.

C Static type checking requires explicit type declarations; dynamic type checking does not require them.

D Dynamic type checking is faster because it checks types before compilation.

💡 Hint

Consider when types are checked and if declarations are mandatory.

Static type checking usually requires explicit type declarations, while dynamic type checking infers types at runtime.

❓ Reasoning

expert

Type Checking in Polymorphism

In a language with subtype polymorphism, which rule ensures type safety during method calls?

A The method argument types in the subtype must be exactly the same as in the supertype.

B The method return type in the subtype can be a subtype of the return type in the supertype.

C The subtype can remove method parameters to simplify the interface.

D The subtype can change method argument types to unrelated types.

💡 Hint

Think about how method overriding respects types to maintain safety.

Covariant return types allow the subtype method to return a more specific type, preserving type safety.

Practice

1. What is the main purpose of type checking rules in a compiler?

easy

A. To ensure that data types are used correctly in operations and assignments

B. To optimize the program's execution speed

C. To translate code into machine language

D. To manage memory allocation during runtime

Solution

1. Step 1: Understand the role of type checking

   Type checking rules verify that variables and expressions use compatible data types to avoid errors.

2. Step 2: Differentiate from other compiler tasks

   Optimization, translation, and memory management are separate compiler tasks, not type checking.

3. Final Answer:

   To ensure that data types are used correctly in operations and assignments -> Option A

4. Quick Check:

   Type checking = Correct data types [OK]

Hint: Type checking = matching data types in code [OK]

Common Mistakes:

• Confusing type checking with code optimization
• Thinking type checking manages memory
• Assuming type checking translates code

2. Which of the following is a correct type checking rule for assignment statements?

easy

A. Type checking only applies to function calls, not assignments

B. A variable can be assigned a value of any type without restrictions

C. Variables do not need to be declared before assignment

D. The type of the value assigned must match the variable's declared type

Solution

1. Step 1: Review assignment type rules

   In type checking, the value assigned must have the same type as the variable's declared type.

2. Step 2: Eliminate incorrect options

   Allowing any type or ignoring declarations violates type safety; type checking applies to assignments.

3. Final Answer:

   The type of the value assigned must match the variable's declared type -> Option D

4. Quick Check:

   Assignment types must match [OK]

Hint: Assignment value type = variable type [OK]

Common Mistakes:

• Ignoring variable declarations
• Assigning incompatible types
• Thinking type checking excludes assignments

3. Consider this code snippet:

int x = 5;
float y = 3.2;
x = y;

What will a strict type checker report?

medium

A. No error, assignment allowed

B. Warning but allowed at runtime

C. Type mismatch error: cannot assign float to int

D. Syntax error due to missing semicolon

Solution

1. Step 1: Identify variable types and assignment

   Variable x is int, y is float. Assignment tries to put a float into an int.

2. Step 2: Apply strict type checking rules

   Strict type checking disallows assigning a float value to an int variable without explicit conversion.

3. Final Answer:

   Type mismatch error: cannot assign float to int -> Option C

4. Quick Check:

   Float to int assignment = error [OK]

Hint: Assigning float to int causes type mismatch error [OK]

Common Mistakes:

• Assuming implicit conversion is automatic
• Confusing syntax errors with type errors
• Ignoring strict type checking rules

4. Identify the error in this code snippet under type checking rules:

string name = "Alice";
int age = "30";

medium

A. No error, both assignments are valid

B. Type error: assigning string literal to int variable

C. Syntax error: missing quotes around 30

D. Runtime error due to invalid conversion

Solution

1. Step 1: Analyze variable declarations and assignments

   name is a string assigned a string literal, which is correct. age is an int assigned a string literal "30".

2. Step 2: Apply type checking rules

   Assigning a string literal to an int variable violates type checking rules, causing a type error.

3. Final Answer:

   Type error: assigning string literal to int variable -> Option B

4. Quick Check:

   String to int assignment = type error [OK]

Hint: Assigning string to int causes type error [OK]

Common Mistakes:

• Thinking quotes around 30 are optional
• Confusing syntax errors with type errors
• Assuming implicit conversion from string to int

5. Given a function with parameters typed as int and float, which call violates type checking rules?

void process(int a, float b) { /*...*/ }

// Calls:
process(10, 5.5);
process(3.2, 4.1);
process(7, 2);

hard

A. process(3.2, 4.1);

B. process(10, 5.5);

C. process(7, 2);

D. All calls are valid

Solution

1. Step 1: Check parameter types for each call

   Function expects int then float. Call 1 passes int and float correctly. Call 2 passes float then float, which mismatches first parameter. Call 3 passes int and int, which may be allowed if int converts to float.

2. Step 2: Apply strict type checking

   Call 2 violates type checking because first argument is float but expected int. Call 3 is valid if implicit int to float conversion allowed for second parameter.

3. Final Answer:

   process(3.2, 4.1); -> Option A

4. Quick Check:

   First param must be int, call 2 fails [OK]

Hint: First argument must be int, float causes error [OK]

Common Mistakes:

• Assuming all numeric types are interchangeable
• Ignoring parameter order in function calls
• Thinking int cannot convert to float