Define macro - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this macro usage?

Consider the following C code using a macro. What will be printed when this program runs?

C

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

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

A 16

B 7

C Error: macro expansion invalid

D 10

💡 Hint

Remember how macros expand without parentheses around parameters.

The macro expands to a + 1 * a + 1. With a=3, due to operator precedence (* before +), it evaluates to 3 + (1 * 3) + 1 = 3 + 3 + 1 = 7.

❓ Predict Output

intermediate

What is the output of this corrected macro?

Now consider this corrected macro definition. What will be printed?

C

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

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

A Error: macro expansion invalid

B 10

C 16

D 7

💡 Hint

Parentheses in macros help control the order of operations.

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

❓ Predict Output

advanced

What is the output of this macro with side effects?

Look at this code using a macro that doubles a value. What will be printed?

C

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

int main() {
    int i = 2;
    printf("%d\n", DOUBLE(i++));
    return 0;
}

A Undefined behavior or unexpected result

B 5

C 4

D 6

💡 Hint

Macros can cause expressions to be evaluated multiple times.

The macro expands to ((i++) + (i++)), so i++ is evaluated twice, causing side effects and undefined or unexpected results.

🧠 Conceptual

advanced

What does this macro do?

Given the macro below, what is its purpose?

C

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

A Returns the sum of a and b

B Returns the smaller of a and b

C Returns true if a equals b

D Returns the larger of a and b

💡 Hint

Look at the conditional operator ? :

The macro compares a and b and returns the one that is greater.

🔧 Debug

expert

Why does this macro cause a compilation error?

Examine the macro and code below. Why does it cause a compilation error?

C

#define INCREMENT(x) x++

int main() {
    int a = 5;
    int b = INCREMENT(a) * 2;
    return 0;
}

A Because macro expansion lacks parentheses causing wrong operator precedence

B Because x++ cannot be used inside macros

C Because the macro is missing a semicolon

D Because multiplication operator * is invalid here

💡 Hint

Think about how the macro expands and operator precedence.

The macro expands to a++ * 2 which is parsed as (a++) * 2, but without parentheses around x++, it can cause unexpected behavior or warnings. The main issue is lack of parentheses causing operator precedence problems.