Parameter passing mechanisms in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the parameter passing mechanism where the actual parameter's value is copied to the formal parameter.

Compiler Design

In [1], changes made to the parameter inside the function do not affect the original argument.

Drag options to blanks, or click blank then click option'

Acall by reference

Bcall by name

Ccall by value

Dcall by result

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing call by value with call by reference, which allows changes to affect the original.

Call by value means the function receives a copy of the argument's value. Changes inside the function do not affect the original variable.

2fill in blank

medium

Complete the code to identify the parameter passing mechanism where the function can modify the caller's variable directly.

Compiler Design

In [1], the function receives the address of the actual parameter, allowing direct modification.

Drag options to blanks, or click blank then click option'

Acall by value

Bcall by reference

Ccall by copy-restore

Dcall by name

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up call by reference with call by value, which does not allow changes to the original variable.

Call by reference passes the address of the variable, so the function can change the original variable's value.

3fill in blank

hard

Fix the error in the statement describing call by name parameter passing.

Compiler Design

In call by name, the actual parameter is [1] each time it is used in the function body.

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Are-evaluated

Bpassed as a copy

Cevaluated once at the start

Dpassed by address

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming call by name evaluates the parameter only once like call by value.

In call by name, the actual parameter expression is re-evaluated every time it is accessed inside the function.

4fill in blank

hard

Fill both blanks to complete the description of call by copy-restore mechanism.

Compiler Design

In call by copy-restore, the actual parameter is [1] to the function and [2] back to the caller after the function finishes.

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Acopied

Bpassed by reference

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing copy-restore with call by reference or call by value.

In call by copy-restore, the value is copied into the function at the start and copied back to the original variable after the function ends.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that maps parameter passing mechanisms to their key feature.

Compiler Design

features = { [1]: [2] for [3] in ['call by value', 'call by reference', 'call by name'] }

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Amechanism

B{'call by value': 'copy', 'call by reference': 'address', 'call by name': 're-evaluation'}[mechanism]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for keys and values incorrectly.

This dictionary comprehension creates a mapping from each parameter passing mechanism to its main characteristic.

Practice

1. Which parameter passing mechanism sends a copy of the argument to the function, so changes inside the function do not affect the original variable?

easy

A. Pass by name

B. Pass by reference

C. Pass by value

D. Pass by result

Solution

1. Step 1: Understand pass by value

   Pass by value means the function receives a copy of the argument, so any changes inside the function do not affect the original variable.

2. Step 2: Compare with other mechanisms

   Pass by reference sends the original variable, so changes affect it. Pass by name and result behave differently and are less common.

3. Final Answer:

   Pass by value -> Option C

4. Quick Check:

   Copy sent, original unchanged = Pass by value [OK]

Hint: Copy means pass by value, original means pass by reference [OK]

Common Mistakes:

• Confusing pass by value with pass by reference
• Thinking pass by name sends a copy
• Assuming pass by result is the same as pass by value

2. Which of the following is the correct syntax to declare a function parameter passed by reference in C++?

easy

A. void func(int &x);

B. void func(int x);

C. void func(ref int x);

D. void func(*int x);

Solution

1. Step 1: Recall C++ reference syntax

   In C++, passing by reference uses the ampersand (&) symbol after the type in the parameter list.

2. Step 2: Analyze options

   void func(int &x); uses int &x which is correct. void func(int x); passes by value, C is invalid syntax, and D is pointer syntax, not reference.

3. Final Answer:

   void func(int &x); -> Option A

4. Quick Check:

   C++ reference uses & in parameter [OK]

Hint: Look for & symbol in parameter for C++ reference [OK]

Common Mistakes:

• Confusing pointer (*) with reference (&)
• Using invalid 'ref' keyword in C++
• Assuming no symbol means pass by reference

3. Consider the following pseudocode using pass by reference:

function increment(x) {
  x = x + 1
}

var a = 5
increment(a)
print(a)

What will be the output?

medium

A. 5

B. Undefined

C. Error

D. 6

Solution

1. Step 1: Understand pass by reference effect

   Since x is passed by reference, the function changes the original variable a by adding 1.

2. Step 2: Trace the code execution

   a starts at 5, increment adds 1 making it 6, then print outputs 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   Pass by reference changes original = 6 [OK]

Hint: Pass by reference changes original variable [OK]

Common Mistakes:

• Assuming pass by reference behaves like pass by value
• Thinking the original variable remains unchanged
• Ignoring the effect of increment inside the function

4. Identify the error in this code snippet using pass by value:

function swap(x, y) {
  temp = x
  x = y
  y = temp
}

var a = 3
var b = 4
swap(a, b)
print(a, b)

medium

A. Print statement is incorrect

B. swap function does not swap original variables

C. Variables a and b are not declared

D. Syntax error in function definition

Solution

1. Step 1: Understand pass by value behavior in swap

   Since parameters are passed by value, swap changes only local copies x and y, not original a and b.

2. Step 2: Check the output effect

   After swap call, a and b remain 3 and 4, so swap does not work as intended.

3. Final Answer:

   swap function does not swap original variables -> Option B

4. Quick Check:

   Pass by value means original unchanged [OK]

Hint: Pass by value swaps local copies only [OK]

Common Mistakes:

• Assuming swap changes original variables with pass by value
• Looking for syntax errors where none exist
• Ignoring parameter passing mechanism effect

5. You want to write a function that modifies a list of numbers by doubling each element. Which parameter passing mechanism is best to use to ensure the original list is changed efficiently?

hard

A. Pass by reference

B. Pass by value

C. Pass by name

D. Pass by result

Solution

1. Step 1: Consider efficiency and effect on original list

   Pass by value copies the entire list, which is inefficient and changes won't affect original.

2. Step 2: Choose mechanism that modifies original efficiently

   Pass by reference sends the original list, allowing direct modification without copying.

3. Final Answer:

   Pass by reference -> Option A

4. Quick Check:

   Modify original efficiently = Pass by reference [OK]

Hint: Modify original data efficiently with pass by reference [OK]

Common Mistakes:

• Choosing pass by value and expecting original change
• Confusing pass by name with pass by reference
• Ignoring efficiency of copying large data