Extern storage class - Mini Project: Build & Apply

Using the extern Storage Class in C

📖 Scenario: You are working on a simple C program split into two files. One file holds a variable, and the other file uses that variable. To share the variable between files, you use the extern storage class.

🎯 Goal: Build a program with two files where one file declares a variable and the other file accesses it using extern. You will see how extern helps share variables across files.

📋 What You'll Learn

Create a global variable count in one file

Declare extern int count; in the other file

Modify count in the second file

Print the updated count value in the second file

💡 Why This Matters

🌍 Real World

Sharing variables across multiple files is common in large C programs to organize code and data.

💼 Career

Understanding <code>extern</code> is essential for working on multi-file C projects, embedded systems, and system programming.

1

Create a global variable in file1.c

In file1.c, create a global integer variable called count and set it to 10.

C

# Your code here

Need a hint?

Global variables are declared outside any function.

2

Declare extern variable in file2.c

In file2.c, declare the variable count using extern int count; to tell the compiler it is defined elsewhere.

C

# Your code here

Need a hint?

The extern keyword tells the compiler the variable is defined in another file.

3

Modify count in file2.c

In file2.c, write a function called increment that adds 5 to count.

C

extern int count;

// Your code here

Need a hint?

Functions can change the value of global variables.

4

Print the updated count in file2.c

In file2.c, write a main function that calls increment() and then prints the value of count using printf.

C

extern int count;

void increment() {
    count += 5;
}

// Your code here

Need a hint?

Remember to include stdio.h to use printf.