Defensive programming practices - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the pointer is NULL before using it.

C

if ([1] != NULL) {
    printf("Pointer is valid.\n");
}

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

Aptr

BNULL

C0

Dptr == NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing NULL to NULL instead of the pointer variable.

Using 'ptr == NULL' inside the if condition which checks for non-null.

We check if the pointer ptr is not NULL before using it to avoid errors.

2fill in blank

medium

Complete the code to safely open a file and check if it opened successfully.

C

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

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

ANULL

Bfopen

Cfile

Ddata.txt

Attempts:

3 left

💡 Hint

Common Mistakes

Checking fopen directly instead of the file pointer variable.

Comparing the filename string to NULL.

We check if file is NULL to know if fopen failed.

3fill in blank

hard

Fix the error in the code to prevent buffer overflow by limiting input size.

C

char buffer[10];
printf("Enter text: ");
scanf("%[1]s", buffer);

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

A10

Bs

C99

D9

Attempts:

3 left

💡 Hint

Common Mistakes

Using %s without size limit causes buffer overflow.

Using %10s reads 10 characters but buffer can only hold 10 including null terminator.

Using %9s limits input to 9 characters plus the null terminator, preventing overflow.

4fill in blank

hard

Fill both blanks to safely allocate memory and check if allocation succeeded.

C

int *arr = (int *)malloc([1] * sizeof(int));
if (arr [2] NULL) {
    printf("Memory allocation failed.\n");
}

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

A10

B==

C!=

Dsizeof

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking if malloc returned NULL.

Using '!=' instead of '==' in the if condition.

Allocate memory for 10 integers and check if arr is NULL to detect failure.

5fill in blank

hard

Fill all three blanks to safely copy a string with length check.

C

char src[] = "Hello";
char dest[6];
if (strlen(src) [1] sizeof(dest) - 1) {
    strncpy(dest, src, [2]);
    dest[[3]] = '\0';
} else {
    printf("Source string too long.\n");
}

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

A<=

Bsizeof(dest) - 1

Cstrlen(src)

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Not adding null terminator after strncpy.

Using wrong comparison operator causing buffer overflow.

Check if source length is less or equal to destination size minus 1, copy that many characters, and add null terminator at last index.