Programming in C using gcc in Linux

Installing GCC and Writing Your First C Program

1️⃣ Check Whether GCC Is Installed

If you are using Linux or UNIX, check if GCC is installed:

$ gcc -v

• If GCC is installed, version details will be displayed.

• If not installed, install it using instructions from:
  https://gcc.gnu.org/install/

---

2️⃣ Install GCC on Ubuntu

Method 1: Install GCC Directly

Open terminal and run:

$ sudo apt-get install gcc

(Example: Ubuntu 18.04 Bionic Beaver / 20.04 Focal Fossa)

---

Method 2: Install Using build-essential (Recommended)

This installs:

• gcc compiler

• g++ compiler

• required libraries

$ sudo apt-get install build-essential

---

3️⃣ Check GCC Version After Installation

$ gcc --version

---

4️⃣ Writing Your First C Program

Example Program

/* my first program */
#include <stdio.h>

int main(void)
{
    printf("Hello World");
    return 0;
}

Output

Hello World

---

5️⃣ Program Explanation (Line by Line)

Line 0

/* my first program */

• Multi-line comments in C are written between /* */

• Comments are ignored by the compiler

• Improve readability and documentation

• Single-line comments use //

---

Line 1

#include <stdio.h>

• Lines starting with # are handled by the preprocessor

• Preprocessor processes header files before compilation

• stdio.h contains declarations for functions like printf()

• Header files usually end with .h

---

Line 2

int main(void)

• Entry point of every C program

• Execution begins from main()

• void → no parameters passed

• int → return type of the function

---

Line 3 & 6

{
}

• Curly brackets define scope

• Used in functions, loops, conditions

• Every function must start and end with { }

---

Line 4

printf("Hello World");

• Standard library function for output

• Semicolon ; marks end of statement

• Mandatory in C

---

6️⃣ Compile and Execute a C Program

Step 1: Save the file

Save as:

hello.c

Step 2: Compile

$ gcc hello.c

• If successful → creates executable:

a.out

---

Step 3: Run Program

$ ./a.out

Output:

Hello World

---

Specify Output File Name Using -o

$ gcc -o hello hello.c
$ ./hello

Output:

Hello World

✔ Ensure:

• gcc is in PATH

• you are in the same directory as hello.c

---

7️⃣ Important GCC Compiler Options

---

1. Specify Output Executable Name (-o)

$ gcc hello.c -o hello

Creates executable named hello.

---

2. Enable All Warnings (-Wall)

$ gcc -Wall hello.c

Shows all compiler warnings.

---

3. Produce Only Preprocessor Output (-E)

$ gcc -E hello.c > hello.i

Generates preprocessed file.

---

4. Produce Assembly Code (-S)

$ gcc -S hello.c > hello.s

Creates assembly output.

---

5. Produce Object File Only (-c)

$ gcc -c hello.c

Creates:

hello.o

(Object/machine-level compiled code without linking)

---

6. Save All Intermediate Files (-save-temps)

$ gcc -save-temps hello.c
$ ls

Output may include:

a.out
hello.c
hello.i
hello.o
hello.s

Stores all compilation stages.

---

7. Link With Shared Libraries (-l)

$ gcc -Wall hello.c -o main -lCPPfile

Links program with shared library libCPPfile.

---

8. Show Verbose Compilation Steps (-v)

$ gcc -Wall -v hello.c -o hello

Displays detailed compilation steps.

---

9. Provide GCC Options From a File (@ option)

Create options file:

$ cat opt_file
-Wall -o hello

Compile using options file:

$ gcc main.c @opt_file

---

8️⃣ Online C Compiler

You can also run C programs online:

https://www.onlinegdb.com/