Macro with arguments - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of macro with arguments

What is the output of this C program?

C

#include <stdio.h>
#define SQUARE(x) x * x

int main() {
    int a = 3;
    int result = SQUARE(a + 1);
    printf("%d\n", result);
    return 0;
}

A 7

B 16

C Error: macro expansion

D 10

💡 Hint

Remember how macros expand without parentheses around arguments.

The macro expands to a + 1 * a + 1 which is 3 + 1 * 3 + 1 = 3 + 3 + 1 = 7, but operator precedence causes multiplication before addition, so it is 3 + (1 * 3) + 1 = 7. However, the macro is SQUARE(x) x * x, so SQUARE(a + 1) expands to a + 1 * a + 1 which is 3 + 1 * 3 + 1 = 7. The output is 7, so option A is correct.

❓ Predict Output

intermediate

Correct macro usage with parentheses

What is the output of this C program?

C

#include <stdio.h>
#define SQUARE(x) ((x) * (x))

int main() {
    int a = 3;
    int result = SQUARE(a + 1);
    printf("%d\n", result);
    return 0;
}

A Error: macro expansion

B 7

C 10

D 16

💡 Hint

Parentheses in macros help control operator precedence.

The macro expands to ((a + 1) * (a + 1)) which is (4 * 4) = 16.

🔧 Debug

advanced

Identify the error in macro with arguments

What error does this code produce when compiled?

C

#include <stdio.h>
#define MAX(a, b) a > b ? a : b

int main() {
    int x = 5, y = 10;
    int max_val = MAX(x, y);
    printf("%d\n", max_val);
    return 0;
}

A Prints 5

B Prints 10

C Syntax error due to missing parentheses

D Runtime error

💡 Hint

Check how the macro expands and operator precedence.

The macro expands to x > y ? x : y which is 5 > 10 ? 5 : 10, so it prints 10. No syntax error occurs here.

❓ Predict Output

advanced

Macro side effects with arguments

What is the output of this C program?

C

#include <stdio.h>
#define INCREMENT(x) (x + 1)

int main() {
    int a = 5;
    int result = INCREMENT(a++) * 2;
    printf("%d %d\n", result, a);
    return 0;
}

A 12 6

B 14 7

C 13 7

D Undefined behavior

💡 Hint

Macros can cause unexpected side effects when arguments have increments.

The macro expands to (a++ + 1) * 2. a++ (post-increment) evaluates to the current value 5, 5 + 1 = 6, then 6 * 2 = 12, and a is incremented to 6 afterward. Prints '12 6'. The argument is evaluated only once, so no undefined behavior.

🧠 Conceptual

expert

Why use parentheses in macro arguments?

Which option best explains why parentheses are important around macro arguments and the entire macro body?

A To allow the macro to accept multiple arguments

B To make the macro run faster at runtime

C To ensure the macro expands to a single expression and respects operator precedence

D To prevent the macro from being replaced by the preprocessor

💡 Hint

Think about how expressions combine when macros are expanded.

Parentheses ensure that when the macro is expanded, the expression behaves as intended by controlling the order of operations and grouping the entire expression.

Practice

1. What does a macro with arguments in C do?

easy

A. It replaces code snippets with given values before compilation

B. It creates a new function at runtime

C. It allocates memory dynamically

D. It executes code conditionally during runtime

Solution

1. Step 1: Understand macro replacement

   Macros with arguments are replaced by the preprocessor before the program runs, substituting the macro call with the code snippet using the given arguments.

2. Step 2: Differentiate from functions

   Unlike functions, macros do not create executable code at runtime but perform textual substitution during compilation.

3. Final Answer:

   It replaces code snippets with given values before compilation -> Option A

4. Quick Check:

   Macro = code substitution before compile [OK]

Hint: Macros replace code before running, not at runtime [OK]

Common Mistakes:

• Thinking macros create functions
• Confusing macros with runtime code
• Assuming macros allocate memory

2. Which of the following is the correct syntax for defining a macro with two arguments a and b that adds them?

easy

A. #define ADD(a, b) a + b

B. #define ADD a, b (a + b)

C. #define ADD(a, b) (a + b)

D. #define ADD(a, b) {a + b}

Solution

1. Step 1: Check macro argument syntax

   Macro arguments must be enclosed in parentheses immediately after the macro name, like ADD(a, b).

2. Step 2: Ensure proper expression grouping

   To avoid operator precedence issues, the expression should be enclosed in parentheses: (a + b).

3. Final Answer:

   #define ADD(a, b) (a + b) -> Option C

4. Quick Check:

   Correct macro syntax = #define NAME(args) (expression) [OK]

Hint: Always put parentheses around macro arguments and whole expression [OK]

Common Mistakes:

• Missing parentheses around arguments
• Not enclosing expression in parentheses
• Using braces {} instead of parentheses

3. Given the macro definition #define SQUARE(x) x * x, what is the output of printf("%d", SQUARE(3 + 1));?

medium

A. Error

B. 16

C. 12

D. 7

Solution

1. Step 1: Expand the macro with argument

   The macro call SQUARE(3 + 1) expands to 3 + 1 * 3 + 1 because the macro definition lacks parentheses around the expression.

2. Step 2: Apply operator precedence

   Multiplication has higher precedence, so 3 + (1 * 3) + 1 = 3 + 3 + 1 = 7.

3. Final Answer:

   7 -> Option D

4. Quick Check:

   Without parentheses, macro expands incorrectly = 7 [OK]

Hint: Without parentheses, macro args can cause wrong math [OK]

Common Mistakes:

• Assuming macro adds parentheses automatically
• Ignoring operator precedence
• Expecting 16 as square of 4

4. Identify the error in this macro definition: #define MULTIPLY(a, b) a * b)

medium

A. Extra closing parenthesis at the end

B. Missing opening parenthesis before a

C. Arguments should not have parentheses

D. Macro name should be lowercase

Solution

1. Step 1: Check parentheses balance

   The macro ends with an extra closing parenthesis ")" that does not match any opening parenthesis.

2. Step 2: Confirm correct macro syntax

   Macro should be defined as #define MULTIPLY(a, b) (a * b) with balanced parentheses around the expression.

3. Final Answer:

   Extra closing parenthesis at the end -> Option A

4. Quick Check:

   Parentheses must be balanced in macro definitions [OK]

Hint: Count parentheses carefully in macro definitions [OK]

Common Mistakes:

• Ignoring unmatched parentheses
• Thinking arguments can't have parentheses
• Believing macro names must be lowercase

5. You want to create a macro MAX(a, b) that returns the larger of two values. Which definition correctly handles expressions as arguments without errors?

hard

A. #define MAX(a, b) ((a > b) ? a : b)

B. #define MAX(a, b) ((a) > (b) ? (a) : (b))

C. #define MAX(a, b) a > b ? a : b

D. #define MAX(a, b) (a > b ? a : b)

Solution

1. Step 1: Understand argument safety

   To safely handle expressions as arguments, each argument must be enclosed in parentheses to avoid precedence errors.

2. Step 2: Check full macro expression grouping

   The entire conditional expression should be enclosed in parentheses to ensure correct evaluation when used in larger expressions.

3. Final Answer:

   #define MAX(a, b) ((a) > (b) ? (a) : (b)) -> Option B

4. Quick Check:

   Parentheses around args and whole expression prevent bugs [OK]

Hint: Always parenthesize macro args and whole expression [OK]

Common Mistakes:

• Missing parentheses around arguments
• Not enclosing entire expression
• Assuming macro works like a function