Multiple input and output in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with multiple input parameters

What is the output of this C program when calling sum_and_product(3, 4, &sum, &product);?

C

#include <stdio.h>

void sum_and_product(int a, int b, int *sum, int *product) {
    *sum = a + b;
    *product = a * b;
}

int main() {
    int sum = 0, product = 0;
    sum_and_product(3, 4, &sum, &product);
    printf("Sum = %d, Product = %d\n", sum, product);
    return 0;
}

A Sum = 7, Product = 12

B Sum = 12, Product = 7

C Sum = 3, Product = 4

D Sum = 0, Product = 0

💡 Hint

Remember that pointers allow functions to modify variables outside their scope.

The function calculates sum and product and stores them via pointers. So sum = 3 + 4 = 7 and product = 3 * 4 = 12.

❓ Predict Output

intermediate

Output of function returning multiple values via struct

What will be printed by this program?

C

#include <stdio.h>

typedef struct {
    int sum;
    int diff;
} Result;

Result calculate(int x, int y) {
    Result r;
    r.sum = x + y;
    r.diff = x - y;
    return r;
}

int main() {
    Result res = calculate(10, 4);
    printf("Sum: %d, Difference: %d\n", res.sum, res.diff);
    return 0;
}

A Sum: 4, Difference: 10

B Sum: 6, Difference: 14

C Sum: 14, Difference: 6

D Sum: 10, Difference: 4

💡 Hint

Check how sum and difference are calculated inside the struct.

Sum is 10 + 4 = 14 and difference is 10 - 4 = 6, stored in the struct and printed.

❓ Predict Output

advanced

Output of function with multiple pointer parameters and side effects

What is the output of this program?

C

#include <stdio.h>

void update_values(int *a, int *b) {
    *a = *a + *b;
    *b = *a - *b;
}

int main() {
    int x = 5, y = 3;
    update_values(&x, &y);
    printf("x = %d, y = %d\n", x, y);
    return 0;
}

A x = 8, y = 3

B x = 8, y = 5

C x = 5, y = 3

D x = 3, y = 5

💡 Hint

Trace the pointer updates step by step.

Initially x=5, y=3. After *a = *a + *b, x=8. Then *b = *a - *b = 8 - 3 = 5. So x=8, y=5.

❓ Predict Output

advanced

Output of function returning multiple outputs via array parameters

What will this program print?

C

#include <stdio.h>

void min_max(int arr[], int size, int *min, int *max) {
    *min = arr[0];
    *max = arr[0];
    for (int i = 1; i < size; i++) {
        if (arr[i] < *min) *min = arr[i];
        if (arr[i] > *max) *max = arr[i];
    }
}

int main() {
    int numbers[] = {7, 2, 9, 4, 5};
    int minimum, maximum;
    min_max(numbers, 5, &minimum, &maximum);
    printf("Min: %d, Max: %d\n", minimum, maximum);
    return 0;
}

A Min: 7, Max: 5

B Min: 2, Max: 7

C Min: 4, Max: 9

D Min: 2, Max: 9

💡 Hint

Look carefully at how min and max are updated in the loop.

The smallest number is 2 and the largest is 9 in the array.

🧠 Conceptual

expert

Why use pointers for multiple outputs in C functions?

Which is the main reason C functions use pointers to return multiple outputs instead of returning multiple values directly?

A Because C functions can only return one value, pointers allow modifying variables outside the function to simulate multiple outputs.

B Because pointers make the program run faster by avoiding copying values.

C Because pointers automatically allocate memory for multiple return values.

D Because pointers prevent any changes to the original variables passed to the function.

💡 Hint

Think about how many values a C function can return directly.

C functions can return only one value directly. Using pointers allows the function to change variables outside its scope, effectively returning multiple outputs.