Function declaration and definition - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple function call

What is the output of this C program?

C

#include <stdio.h>

int add(int a, int b);

int main() {
    int result = add(3, 4);
    printf("%d\n", result);
    return 0;
}

int add(int a, int b) {
    return a + b;
}

A 7

B 34

C 0

D Compilation error

💡 Hint

Look at what the function 'add' returns and what is printed.

The function 'add' returns the sum of its two parameters. Calling add(3,4) returns 7, which is printed.

❓ Predict Output

intermediate

Function declaration without definition

What happens when you compile and run this C code?

C

#include <stdio.h>

int multiply(int x, int y);

int main() {
    printf("%d\n", multiply(2, 3));
    return 0;
}

A Linker error

B 0

C 6

D Compilation error

💡 Hint

The function is declared but not defined anywhere.

The compiler knows the function signature but the linker cannot find the function's code, causing a linker error.

🔧 Debug

advanced

Identify the error in function definition

What error does this code produce?

C

#include <stdio.h>

int square(int n) {
    return n * n;
}

int main() {
    printf("%d\n", square(5));
    return 0;
}

A Undefined function 'square' (Linker error)

B No error, outputs 25

C Type mismatch error

D Missing semicolon after return statement (SyntaxError)

💡 Hint

Check punctuation at the end of the return line.

The return statement now has a semicolon, so the code compiles and outputs 25.

❓ Predict Output

advanced

Function with pointer parameter output

What is the output of this program?

C

#include <stdio.h>

void increment(int *p) {
    (*p)++;
}

int main() {
    int a = 10;
    increment(&a);
    printf("%d\n", a);
    return 0;
}

A Compilation error

B 10

C 11

D Garbage value

💡 Hint

The function changes the value at the address passed.

The function increments the value pointed to by p, so a becomes 11.

🧠 Conceptual

expert

Function declaration and definition order

Which option correctly explains why this code compiles and runs without errors?

C

#include <stdio.h>

void greet();

int main() {
    greet();
    return 0;
}

void greet() {
    printf("Hello!\n");
}

A Because the function is defined before main, so no declaration is needed.

B Because the function is declared after main, so the compiler ignores the call.

C Because the function is defined inside main, so it is local and accessible.

D Because the function is declared before main and defined after, the compiler knows its signature when main calls it.

💡 Hint

Think about how the compiler processes declarations and definitions.

The declaration before main tells the compiler the function signature, so the call in main is valid. The definition after main provides the actual code.