From Compilation to Program Structure

What is written inside a C program?

We already know that a compiler translates C code. Now we will study the structure of that code.

Where does execution of a C program normally begin?

Begin with the earlier flow: C Source Code → Compiler → Executable → Output. Ask students what they recognize in the code shown on the right.

first_program.c

#include <stdio.h>

int main(void)
{
    printf("Hello, Students!");

    return 0;
}

Build the program

Basic Structure of a C Program

A C program is organized into clearly defined sections.

hello.cStep 1 of 6

Step 1

Do not reveal the full program immediately. Pause at every step and ask what students think the next line should be.

Program Anatomy

Sections of a C Program

circle_area.cProgram sections

/* Program to calculate circle area */
#include <stdio.h>
#define PI 3.14159
int main(void)
{
    float radius = 2.0f;
    float area = PI * radius * radius;
    printf("Area = %.2f", area);
    return 0;
}
            

Program Structure

Program Anatomy

Each section has a specific purpose in the program.

Most C statements end with a semicolon, but preprocessor directives do not.

Ask students to name the section before clicking. Keep the distinction simple: declaration creates/describes something; a statement performs an action.

The main function

Understanding int main(void)

1

int

The function returns an integer value to the operating environment.

int main(void)

▶

main

Program execution normally begins from the main function.

main

( )

void

This form indicates that no arguments are being received by the function.

(void)

{ }

Braces

They mark the beginning and end of the function body.

;

Semicolon

Most C statements end with a semicolon.

0

return 0;

It ends main() and indicates successful completion.

Use the standard beginner form int main(void). Avoid teaching void main().

Preprocessing Stage

Preprocessing Before Compilation

Directives beginning with # are handled before normal compilation.

C Source File
program.c

→

Preprocessor
handles # directives

→

Expanded Source
directives processed

→

Compiler
translates C code

Core sentence: “The preprocessor handles lines beginning with # before normal compilation.”

Header Inclusion

Using #include

Header files provide declarations required by library functions.

Use stdio.h

Provides the declaration of printf()

include_demo.c

Header is available. Click “Check Program”.

Remember

#include <stdio.h>

Angle brackets are normally used for standard or system headers.

#include "myheader.h"

Quotation marks are commonly used for a header created in our own project.

A preprocessor directive begins with # and normally does not end with a semicolon.

For beginners, say that stdio.h makes the declaration of printf available. Do not say that it copies the whole library.

Macro Definition

Using #define

Choose the value of PI

macro_demo.c

#define PI 3.14159

float radius = 2.0f;
float area = PI * radius * radius;

Expanded line

The preprocessor performs textual replacement before normal compilation.

No = sign and no semicolon are used in this simple object-like macro definition.

Ask students what the line becomes before clicking Replace. Mention that macro names are often written in uppercase by convention.

Common Programming Errors

Incorrect and Correct C Program

Small syntax and structure mistakes can prevent successful compilation.

incorrect.c5 errors

include <stdio.h>

#define VALUE = 10;

void main()
{
    printf("Value = %d", VALUE)
    return 0;
}

Error 1: First line

Error 2: Macro definition

Error 3: main function

Error 4: printf statement

Error 5: Macro punctuation

Five corrections are available.

Let the class work for one minute first. Then reveal one correction at a time.

Program Sequence

Correct Order of a C Program

The program sections follow a logical and readable order.

Available lines

Your program

This checks whether students remember the order: include, main, opening brace, statement, return, closing brace.

Knowledge Review

C Program Structure and Preprocessor Quiz

Question 1 of 6

Ask students to answer aloud before clicking. Repeat any item answered incorrectly by most of the class.

One-minute recap

Remember this structure

Comments

→

#include / #define

→

main() Function

→

Statements + return 0;

Preprocessor directives are handled before normal compilation, and program execution normally begins from main().

Finish by asking students to write the complete Hello Students program without looking at the screen.