Why error handling is needed in C - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the file opened successfully.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("data.txt", "r");
    if (file == [1]) {
        printf("Failed to open file.\n");
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

ANULL

B0

C1

DEOF

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if file == 0 instead of NULL

Not checking the file pointer at all

In C, fopen returns NULL if the file cannot be opened. Checking if file == NULL helps detect errors.

2fill in blank

medium

Complete the code to handle division by zero error.

C

#include <stdio.h>

int main() {
    int a = 10, b = 0;
    if (b [1] 0) {
        printf("Error: Division by zero!\n");
    } else {
        printf("Result: %d\n", a / b);
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A==

B!=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '=='

Not checking divisor before division

To avoid division by zero, check if the divisor b is equal to zero before dividing.

3fill in blank

hard

Fix the error in the code to properly handle file reading errors.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("input.txt", "r");
    char buffer[100];
    if (file == [1]) {
        perror("Error opening file");
        return 1;
    }
    if (fgets(buffer, sizeof(buffer), file) == [2]) {
        perror("Error reading file");
    }
    fclose(file);
    return 0;
}

Drag options to blanks, or click blank then click option'

A-1

BEOF

C0

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Checking fgets result against EOF instead of NULL

Using 0 or -1 incorrectly

fopen returns NULL on failure; fgets returns NULL on failure or end of file. Checking against NULL detects errors.

4fill in blank

hard

Fill both blanks to handle memory allocation errors.

C

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = (int *)malloc(sizeof(int) * 10);
    if (ptr == [1]) {
        printf("Memory allocation failed.\n");
        return [2];
    }
    free(ptr);
    return 0;
}

Drag options to blanks, or click blank then click option'

ANULL

B1

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking malloc result

Returning 0 on error

malloc returns NULL if memory allocation fails. Returning 1 indicates an error exit status.

5fill in blank

hard

Fill all three blanks to handle user input errors safely.

C

#include <stdio.h>

int main() {
    int number;
    printf("Enter a number: ");
    if (scanf("%d", &number) != [1]) {
        printf("Invalid input!\n");
        return [2];
    }
    if (number [3] 0) {
        printf("You entered: %d\n", number);
        return 0;
    }
    printf("Number must be positive.\n");
    return 1;
}

Drag options to blanks, or click blank then click option'

A0

B1

C>

Attempts:

3 left

💡 Hint

Common Mistakes

Checking scanf result against 0

Not validating positive number

Returning 0 on error

scanf returns the number of successfully read items, so it should be 1. Return 1 for error. Check if the number is greater than zero for positivity.