Function calling - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested function calls

What is the output of this C program when run?

C

#include <stdio.h>

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

int multiply(int x, int y) {
    return x * y;
}

int main() {
    int result = multiply(add(2, 3), add(4, 1));
    printf("%d\n", result);
    return 0;
}

A 15

B 20

C 25

D 10

💡 Hint

Remember to evaluate the inner add() calls before multiply().

The add(2, 3) returns 5, add(4, 1) returns 5, then multiply(5, 5) returns 25.

❓ Predict Output

intermediate

Function call with pointer argument

What will be printed by this C program?

C

#include <stdio.h>

void update(int *p) {
    *p = *p + 10;
}

int main() {
    int val = 5;
    update(&val);
    printf("%d\n", val);
    return 0;
}

A 15

B 10

C 5

D 0

💡 Hint

The function changes the value at the pointer's address.

The function adds 10 to the value pointed by p, so val becomes 15.

❓ Predict Output

advanced

Output of recursive function call

What is the output of this C program?

C

#include <stdio.h>

int factorial(int n) {
    if (n == 0) return 1;
    else return n * factorial(n - 1);
}

int main() {
    printf("%d\n", factorial(4));
    return 0;
}

A 120

B 10

C 16

D 24

💡 Hint

Factorial of 4 is 4*3*2*1.

factorial(4) = 4*factorial(3) = 4*3*2*1 = 24.

❓ Predict Output

advanced

Output with function pointer call

What does this C program print?

C

#include <stdio.h>

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

int main() {
    int (*func_ptr)(int) = square;
    int val = 3;
    printf("%d\n", func_ptr(val));
    return 0;
}

A 9

B 6

C 3

D 0

💡 Hint

Function pointers can be called like normal functions.

func_ptr points to square, so func_ptr(3) returns 9.

❓ Predict Output

expert

Output of function call with side effects and order

What is the output of this C program?

C

#include <stdio.h>

int f(int *x) {
    (*x)++;
    return *x;
}

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

A 12

B 13

C 11

D 10

💡 Hint

The order of evaluation of function arguments is unspecified in C.

Depending on order, f(&a) increments a twice. If left call evaluated first: f(&a) increments a to 6 returns 6, second call increments to 7 returns 7, sum 13.