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.