This document provides an introduction and overview of the C programming language. It discusses that C was developed in 1972 and became popular for writing operating systems. It then covers basic programming concepts like algorithms, variables, constants, and data types. The document explains how to write, compile, and execute a basic C program. It also outlines rules for integer, float, and character constants as well as naming variables. Keywords reserved for C language features are also listed.

1. Introduction to Computers and
Programming (CSC103)
Lecture 03

2. Introduction to C Language
 C is developed at AT&T’s Bell Laboratories of USA in
1972
 Designed and written by Dennis Ritchie
 Gained popularity and support in late 1970
 Most of the Operating Systems are written in C
 American National Standards Institute (ANSI) formed an
ANSI C committee X3J11 in 1983
 In 1990, first official ANSI standard definition was
published
 Why C?Why not C++, Java or C#?
 First have to learn basic learning elements of a language
2

3. Programming
 Computers are dumb machines;They are told what to do
 e.g. How to add two numbers, how to find the average etc
 Basic operations of a computer system form instruction
set
 Solving a problem
 Express the solution in set of instructions
 Program: collection of instructions to solve a specific
problem
 Algorithm: the approach or method that is used to solve a
problem.
3

4.  For example:A program that tests if a number is even or
odd
 Program:The set of statements that solves the problem
 Algorithm:The method that is used to test if a number is even
or odd
 To solve a problem, first express the solution in terms of
an algorithm
 Then develop a program that implements that algorithm
4

5.  Algorithm for solving even and odd number problem:
1) Get the number
2) Divide the number by two (2)
3) If remainder is zero (0), the number is even
4) Otherwise, the number is odd
 This algorithm is then implemented in a specific language
like C, C++, Java,Visual Basic etc
5

6. Learning English Language vs C Language
6

7. C Character Set
 Valid alphabets, numbers and special symbols allowed in C
7

8. My First C Program – with a problem
main()
{
printf("My First C Program");
}
Output:
Compilation Error
8

9. My First C Program – correction
#include<stdio.h>
void main()
{
printf("My First C Program");
}
Output
My First C Program
9

10. Compilation & Execution
 Edit
 Program is first typed into a file
 A text editor like notepad is used
 Save the file with a valid name along with .c extension e.g. prog1.c
 This program is known as source program
 Preprocessor
 Removes comments
 Handles directives for source file inclusions, definitions etc
 Compile
 It examines each program statement in the source program
 Checks the syntax and semantics of the language
 Any error is notified to the user
 Correct the error and restart the compilation process
 Two types of errors
 Syntactic errors (when an invalid statement is written in program)
 Semantic errors (logical error)
10

11.  If there is no error, the compiler translates each
statement into assembly language form.
 Then the assembly language statements are translated
into machine instructions using another program called
assembler
 Sometimes assembler is part of the compiler
 The assembler translated each assembly language
statement into a binary format known as object code
 Object code is written into another file having extension of
”obj” e.g. prog1.obj
 Now the program is ready to be linked
11

12.  Link
 The purpose of linking is to get the program into final form for
execution
 It links other programs if the compiler have used before
 Programs from library are also linked
 The process of compiling and linking is called building
 The final linked file, called executable object code is stored in
another file
 with extension “.exe”
 Execute
 To subsequently execute the program type the name of the
executable file
 Loading is the process of placing the program in computer’s memory
and initiating it’s execution
12

13. Constants, Variables and Keywords
 The alphabets, digits and special symbols when properly
combined form constants, variables and keywords
 A constant is an entity that doesn’t change
 A variable is an entity that may change
 In a program, we do different calculations
 The results of these calculations are stored in computers
memory
 To make the retrieval of these values easy, these memory
locations are given names
 Since the values stored in these memory locations may change
 The names given to these memory locations are called variables
13

14. Example
 For example 3 is stored in a memory location
 The name of this memory location is x
 Then we assign a new value 5 to this memory location
 This will overwrite the earlier value 3, as a memory
location can hold one value at a time
 Since the memory location x can hold different values at
different times
 x is known as a variable
 Value 3 or 5 do not change, hence are known as
constants
14

15. Types of C Constants
 C constants can be divided into two major categories
 Primary Constants
 Secondary Constants
15

16. Rules for Integer Constants
 An integer constant must have at least one digit
 It must not have a decimal point
 It can be either positive or negative
 If no sign precedes an integer constant it is assumed to be
positive
 No commas or blanks are allowed within an integer
constant
 The allowable range for constants is -32768 to 32767
 e.g. 430, +635, -4090
16

17. Rules for Real or Float Constants
 The float constants could be written in two forms
 Fractional form
 Exponential form
Following are the rules for float constants
 A float constant must have at least one digit
 It must have a decimal point
 It could be either positive or negative
 Default sign is positive
 No commas or blanks are allowed within a float constant
 e.g. +534.63, 834.0, -27.50
17

18. Cont…
 In exponential form, the float constant is represented in two
parts.The part appearing before e is called mantissa, whereas
the part after e is called exponent
Following are the rules for exponential form of float constant
 The mantissa and exponential parts should be separated by e
 The mantissa part may have a positive or negative sign
 Default sign of mantissa part is positive
 The exponent must have at least one digit, which must be a
positive or negative integer. Default sign is positive
 Range of float constant in exponential form is -3.4e38 to
3.4e38 (which is 3.4 x 1038)
 e.g. 363e5,+4.2e7, 9.4e-4
18

19. Rules for Character Constants
 A character constant is a single alphabet, a single digit or
a single special symbol enclosed within single inverted
commas
 Both inverted commas should point to the left
 For example, ’A’ is a valid character constant whereas ‘A’
is not
 The maximum length of a character constant can be 1
character
 e.g.‘A’,‘e’,‘5’
19

20. Types of C Variables
 Variable names are given to a location in memory
 These locations can contain integer, float or character
constants
 Types of variables depends on the types of constants that
it can handle
 A particular type of variable can hold only the same type
of constant
 e.g. an integer variable can hold only an integer constant,
a float variable can hold a float constant and a character
variable can hold a character constant
20

21. Constructing a Variable Name
 Constructing the variable names of all types the same set
of rules apply. These rules are given below:
 A variable name is any combination of 1 to 31 alphabets, digits
or underscores
 Some compilers allow variable names of length 247 characters
 Do not create unnecessary long variable names
 The first character in the variable name must be an alphabet or
underscore
 No commas or blanks are allowed within a variable name
 No special characters other than underscore can be used
 e.g. si_int, age_max, value80
21

22.  C compiler distinguish between the variable names by
making it compulsory to declare the type of any variable
you want to use in a program
 Following are some type declaration examples
int sum;
float salary;
char name;
22

23. Addition Example
#include<stdio.h>
void main()
{
int sum;
sum = 30 + 40;
printf("The sum of 30 and 40 is %dn", sum);
}
23

24. C Keywords
 Keywords are the words whose meaning has already been explained to the
C compiler
 The keywords cannot be used as variable names
 The keywords are also called “Reserved words”
 There are 32 keywords available in C
24