UNIT - IV - INTRODUCTION TO C - FUNDAMENTAL OF COMPUTER PROGRAMMING

1. UNIT – IV
FUNDAMENTALS OF C PROGRAM

2. INTRODUCTION
• C is a general-purpose programming language that was created in
the early 1970s by Dennis Ritchie at Bell Labs. It’s one of the oldest
and most influential programming languages — many modern
languages like C++, Java, C#, Python, and Go were inspired by it.
• Fast (because it’s close to machine language)
• Portable (can run on different hardware with little modification)
• Powerful (directly manage memory and hardware)

3. STRUCTURE OF THE C PROGRAM
• The basic structure of a C
program is divided into 6
parts which makes it easy to
read, modify, document, and
understand in a particular
format.
• Documentation
• Preprocessor Section
• Definition
• Global Declaration
• Main() Function
• Sub Programs
• // Documentation
• /**
• * file: sum.c
• * author: you
• * description: program to find sum.
• */
• // Link
• #include <stdio.h>
• // Definition
• #define X 20
• // Global Declaration
• int sum(int y);
• // Main() Function
• int main(void)
• {
• int y = 55;
• printf("Sum: %d", sum(y));
• return 0;
• }
• // Subprogram
• int sum(int y)
• {
• return y + X;
• }

4. 1. DOCUMENTATION
• This section consists of the description of the program, the name of
the program, and the creation date and time of the program. It is
specified at the start of the program in the form of comments.
Documentation can be represented as:
// description, name of the program, programmer name, date, time etc.
Or
/*description, name of the program, programmer name, date, time etc*/
• Anything written as comments will be treated as documentation of the
program and this will not interfere with the given code. Basically, it
gives an overview to the reader of the program.

5. 2.PREPROCESSOR
• All the header files of the program will be declared
in the preprocessor section of the program.
• Header files help us to access other's improved
code into our code. A copy of these multiple files is
inserted into our program before the process of
compilation.
Example:
#include<stdio.h>
#include<math.h>

6. 3. DEFINITION
• Preprocessors are the programs
that process our source code
before the process of compilation.
• There are multiple steps which are
involved in the writing and
execution of the program.
Preprocessor directives start with
the '#' symbol.
• The #define preprocessor is used
to create a constant throughout the
program. Whenever this name is
encountered by the compiler, it is
replaced by the actual piece of
defined code.
• Example:
#define X 20

7. 4. GLOBAL DECLARATION
• The global declaration
section contains global
variables, function
declaration, and static
variables.
• Variables and functions
which are declared in
this scope can be used
anywhere in the
program.
• Example:
int sum(int y);

8. 5. MAIN() FUNCTION
• Every C program must have a main
function. The main() function of the
program is written in this section.
• Operations like declaration and
execution are performed inside the
curly braces of the main program.
• The return type of the main()
function can be int as well as void
too. void() main tells the compiler
that the program will not return any
value.
• The int main() tells the compiler
that the program will return an
integer value.
• Example:
void main()
int main()

9. 6. SUB PROGRAMS
• User-defined functions are
called in this section of the
program.
• The control of the program
is shifted to the called
function whenever they are
called from the main or
outside the main() function.
• These are specified as per
the requirements of the
programmer.
• Example:
int sum(int x, int y)
{
return x+y;
}

10. KEYWORDS
• Keywords are
predefined or reserved
words that have special
meanings to the
compiler. These are part
of the syntax and cannot
be used as identifiers in
the program
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11. Example
• #include <stdio.h>
• int main() {
• int return = 10;
• printf("%dn",
return);
• return 0;
• }
• /Solution.c: In function
'main':
./Solution.c:4:9: error:
expected identifier or '('
before 'return'
int return = 10;
^
./Solution.c:5:20: error:
expected expression before
'return'
printf("%dn", return);
^

12. Example
• int main() {
• int num = 10; // 'int'
and 'return' are
keywords
• return 0;
• }

13. IDENTIFIERS
• Identifiers are names
given by the
programmer to
variables, functions,
arrays, structures, etc.
• They are user-defined
names
• Examples:
age, sum, totalMarks,
calculateArea, etc.
• int age = 20;
float totalMarks = 89.5;

14. EXAMPLE
• #include <stdio.h>
• int main() {
• int marks = 90; // 'int' →
keyword, 'marks' → identifier
• float average = 85; // 'float' →
keyword, 'average' → identifier
• printf("Marks: %d, Average:
%.2f", marks, average);
• return 0; // 'return' →
keyword
• }
• #include <stdio.h>
• int main() {
• int age = 18;
• float height = 5.6;
• char grade = 'A';
• printf("Age: %dn", age);
• printf("Height: %.1fn", height);
• printf("Grade: %cn", grade);
• return 0;
• }

15. BASIC RULES FOR KEYWORDS
Rule No. Rule Example / Note
1
Keywords are always
lowercase.
✅ int, float ❌ INT, If
2
Keywords cannot be used
as identifiers (variable
names).
❌ int int = 5; (invalid)
3
Keywords have fixed
meaning in C.
int → integer type, if →
conditional statement
4 Total 32 keywords in C.
Examples: int, if, else,
return, while, etc.
5
Keywords cannot be
redefined.
You can’t change what for
or return does.

16. BASIC RULES FOR IDENTIFIERS
Rule No. Rule Example / Note
1
Identifiers must start with
a letter (A–Z or a–z) or
underscore (_).
✅ name, _value
2
After the first letter, they
can contain letters, digits,
or underscores.
✅ age1, total_marks
3 No spaces allowed. ❌ total marks (invalid)
4
No special characters
allowed except
underscore _.
❌ @sum, total$
5
Cannot use keywords as
identifiers.
❌ int for = 10; (invalid)

17. Rule No. Rule Example / Note
6
Case-sensitive —
uppercase and lowercase
are different.
Age ≠ age
7
Length can be long, but
usually only first 31
characters are recognized
by compiler.
totalMarksInExam (valid)
8
Must be meaningful for
better readability.
✅ studentName better than
s
9
You can define unlimited
identifiers.
No restriction like
keywords.

18. VARIABLES
• Variables are containers for storing data values,
like numbers and characters.
• In C, there are different types of variables
(defined with different keywords), for example:
• int - stores integers (whole numbers), without
decimals, such as 123 or -123
• float - stores floating point numbers, with
decimals, such as 19.99 or -19.99
• char - stores single characters, such as 'a' or 'B'.
Characters are surrounded by single quotes
Declaring (Creating) Variables
To create a variable, specify the type and assign
it a value
Syntax
• type variableName = value;
Also declare a variable without assigning the
value, and assign the value later.
int myNum;
myNum=15;

19. DATA TYPES
• Each variable in C has an associated
data type. It specifies the type of
data that the variable can store like
integer, character, floating, double,
etc.
• C is a statically type language
where each variable's type must be
specified at the declaration and once
specified, it cannot be changed.

20. Integer Data Type
• Stores whole numbers
(positive, negative, or
zero).
• We use int keyword to
declare the integer
variable:
• Size: 4 bytes, Range: -
2,147,483,648 to
2,147,483,647.
• Format specifier: %d.
• #include <stdio.h>
• int main() {
• int var = 22;
•
• printf("var = %d",
var);
• return 0;
• }

21. Character Data Type
• Stores a single character
(like ‘A’, ‘b’, or ‘5’).
• Size: 1 byte, Range: -
128 to 127 (signed by
default).
• Format specifier: %c.
• #include <stdio.h>
• int main() {
• char ch = 'A';
•
• printf("ch = %c", ch);
• return 0;
• }

22. Float Data Type
• Stores decimal
numbers (numbers with
fractional part).
• Size: 4 bytes,
Approximate range:
3.4e-38 to 3.4e+38.
• Format specifier: %f.
• #include <stdio.h>
• int main() {
• float val = 12.45;
•
• printf("val = %f", val);
• return 0;
• }

23. Double Data Type
• Stores decimal numbers
with more precision
than float.
• Size: 8 bytes,
Approximate range:
1.7e-308 to 1.7e+308.
• Format specifier: %lf.
• #include <stdio.h>
• int main() {
• double val = 1.4521;
•
• printf("val = %lf", val);
• return 0;
• }

24. EXAMPLE
• #include <stdio.h>
• int main()
• {
• // integer
• int age = 20;
• // floating-point
• float height = 5.7;
• // double-precision floating-
point
• double pi = 3.14159;
• // character
• char grade = 'A';
• printf("Age: %dn", age);
• printf("Height: %.1fn",
height);
• printf("Pi: %.5lfn", pi);
• printf("Grade: %cn",
grade);
• return 0;
• }

25. • #include <stdio.h>
• int main() {
• int a = 10;
• float b = 3.14;
• char c = 'A';
• double d =
123.456789;
• char name[] = "C
Programming";
• printf("Integer: %dn", a);
• printf("Float: %.2fn", b);
• printf("Character: %cn",
c);
• printf("Double: %.3lfn",
d);
• printf("String: %sn",
name);
• return 0;
• }

26. Format Specifiers
• Format specifiers are the symbols
that are used for printing and
scanning values of given data types.
• Format specifiers in C are symbols
used in functions like printf() and
scanf() to tell the compiler what
type of data is being input or output.
• For example, to output the
value of an int variable, use the
format specifier %d surrounded
by double quotes (""), inside
the printf() function
Example
• int myNum = 15;
printf("%d", myNum);

27. Format Specifiers in scanf()
• scanf() is used to read
user input from the
console. It takes the
format string and the
addresses of the
variables where the
input will be stored.
• Syntax
• scanf("formatted_string
",
address_of_variables/va
lues);

28. • #include <stdio.h>
• int main() {
• int age;
• printf("Enter your age: ");
•
• // Reads an integer
• scanf("%d", &age);
•
• // Prints the age
• printf("Age is: %dn", age);
• return 0;
• }
• #include <stdio.h>
• int main() {
• char ch;
• printf("Enter a character: n");
•
• // Reads an Character
• scanf("%c", &ch);
•
• // Prints the Character
• printf("Entered character is: %cn",
ch);
• return 0;
• }

29. • #include <stdio.h>
• int main() {
• int age;
• float weight;
• double height;
• char grade;
• char name[20];
• printf("Enter your name: ");
• scanf("%s", name);
• printf("Enter your age: ");
• scanf("%d", &age);
• printf("Enter your weight (kg):
");
• scanf("%f", &weight);
• printf("Enter your height (m): ");
• scanf("%lf", &height);
• printf("Enter your grade: ");
• scanf(" %c", &grade); // Note space
before %c
• printf("n--- Your Details ---n");
• printf("Name: %snAge: %d
nWeight: %.1f kgnHeight: %.2lf m
nGrade: %cn",
• name, age, weight, height,
grade);
• return 0;
• }