Writing to files in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file named "output.txt" for writing.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("output.txt", "[1]");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }
    fclose(file);
    return 0;
}

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

Aa

Brw

Cw

Dr

Attempts:

3 left

💡 Hint

Common Mistakes

Using "r" mode which is for reading only.

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

Use "w" mode to open a file for writing. It creates the file if it doesn't exist and truncates it if it does.

2fill in blank

medium

Complete the code to write the string "Hello, World!" to the file.

C

#include <stdio.h>

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

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

AHello World

BHello, World!

CHello World!

DHello,World!

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the comma or exclamation mark.

Writing without quotes or incorrect string format.

The string to write is exactly "Hello, World!" including the comma and exclamation mark.

3fill in blank

hard

Fix the error in the code to properly close the file after writing.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("output.txt", "w");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }
    fprintf(file, "Hello, World!\n");
    [1](file);
    return 0;
}

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

Afclose

Bclose

Cfileclose

Dclosefile

Attempts:

3 left

💡 Hint

Common Mistakes

Using close() which is for low-level file descriptors, not FILE pointers.

Using incorrect function names like fileclose or closefile.

Use fclose() to close a file opened with fopen().

4fill in blank

hard

Fill both blanks to write an integer value 42 to the file using fprintf.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("output.txt", "w");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }
    int number = 42;
    fprintf(file, "[1]", [2]);
    fclose(file);
    return 0;
}

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

A"%d"

Bnumber

C"%s"

D42

Attempts:

3 left

💡 Hint

Common Mistakes

Using "%s" which is for strings.

Passing the literal 42 instead of the variable number.

Use the format specifier "%d" to print an integer, and pass the variable number as argument.

5fill in blank

hard

Fill all three blanks to write multiple lines to a file using fprintf inside a loop.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("output.txt", "w");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }
    for (int i = 1; i <= 3; i++) {
        fprintf(file, [1], [2], [3]);
    }
    fclose(file);
    return 0;
}

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

A"Line %d: %s\n"

Bi

C"Hello"

D"Line %d\n"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a format string with only one placeholder.

Passing arguments in wrong order or missing arguments.

The format string "Line %d: %s\n" prints the line number and a string. Pass i and "Hello" as arguments.