File pointers in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file named "data.txt" for reading.

C

#include <stdio.h>

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

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

Aa

Bw

Cr

Drw

Attempts:

3 left

💡 Hint

Common Mistakes

Using "w" which overwrites the file instead of reading.

Using "rw" which is not a valid mode in C.

The mode "r" opens the file for reading. Other modes like "w" are for writing, "a" for appending.

2fill in blank

medium

Complete the code to write the string "Hello" to the file using fprintf.

C

#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "w");
    if (fp == NULL) {
        return 1;
    }
    fprintf(fp, "[1]\n");
    fclose(fp);
    return 0;
}

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

AWorld

BText

CFile

DHello

Attempts:

3 left

💡 Hint

Common Mistakes

Writing a different string than "Hello".

Forgetting to include the newline character if needed.

"Hello" is the string to write to the file as per the instruction.

3fill in blank

hard

Fix the error in the code to correctly read a line from the file into buffer.

C

#include <stdio.h>

int main() {
    char buffer[100];
    FILE *fp = fopen("input.txt", "r");
    if (fp == NULL) {
        return 1;
    }
    fgets([1], 100, fp);
    printf("%s", buffer);
    fclose(fp);
    return 0;
}

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

Abuffer

B&buffer

Cfp

D*buffer

Attempts:

3 left

💡 Hint

Common Mistakes

Using &buffer which is a pointer to the array, not a char pointer.

Using *buffer which is the first character, not a pointer.

fgets expects a pointer to a char array, so passing "buffer" is correct.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

C

#include <stdio.h>
#include <string.h>

int main() {
    char *words[] = {"cat", "elephant", "dog", "giraffe"};
    int lengths[4];
    int count = 0;
    for (int i = 0; i < 4; i++) {
        if (strlen(words[i]) [1] 3) {
            lengths[count] = strlen(words[i]);
            count[2];
        }
    }
    for (int j = 0; j < count; j++) {
        printf("%d\n", lengths[j]);
    }
    return 0;
}

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

A>

B++

C<

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator which selects wrong words.

Decrementing count instead of incrementing.

The condition checks if word length is greater than 3, and count is incremented with ++.

5fill in blank

hard

Fill all three blanks to create a file pointer, open a file for appending, and write a line.

C

#include <stdio.h>

int main() {
    FILE *[1];
    [1] = fopen("log.txt", "[2]");
    if ([1] == NULL) {
        return 1;
    }
    fprintf([1], "Log entry\n");
    fclose([1]);
    return 0;
}

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

Afp

Ba

Dr

Attempts:

3 left

💡 Hint

Common Mistakes

Using "r" mode which opens file for reading only.

Using different variable names inconsistently.

Use variable name "fp" for the file pointer, open file in append mode "a", and use "fp" to write and close.