The document discusses key concepts in the C programming language including its popularity due to being robust, efficient, fast, and portable. It describes C's character set including alphabets, digits, and special symbols that can be used to form constants, variables, and keywords. Constants represent values that do not change, while variables represent unknown values. Keywords are reserved words in C that are predefined like int, long, struct, etc. The document also discusses the structure of a C program including comments, preprocessor directives, declarations, functions, and executable statements. It provides an example of a simple "Hello World" C program to print that message.

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2. Popularity of ‘C’
● Robust
● Efficient and fast
● Portable
● Structured Programming
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3. Character Set
● A character can a number, alphabet, or
any special symbol to represent
information
Alphabets A, B, ….., Y, Z
a, b, ……, y, z
Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Special symbols ~ ‘ ! @ # % ^ & * ( ) _ - + =
|{}[]:;"'<>,.?/
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4. Constants, Variables and
Keywords
● A combination of character set’s
numbers, alphabets and special
symbols forms constants or variable or
keywords
Alphabets, Numbers and Special
Symbols
Constants Variables Keywords
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5. Constants
● A value that does not change during the
execution of programming.
Constants
Primary Secondary
Constants Constants
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6. Variables
● Variables in C have the same meaning as
variables in algebra. That is, they represent
some unknown, or variable, value.
x=a+b
z + 2 = 3(y - 5)
● Remember that variables in algebra are
represented by a single alphabetic
character.
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7. Keywords
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
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8. Program Structure in C
● EACH complete C program is composed of:
● Comment statements
● Pre-processor directives
● Declaration statements
● One or more functions
● Executable statements
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9. C Syntax and Hello World
#include inserts another file. “.h” files are called
“header” files. They contain stuff needed to interface to
libraries and code in other “.c” files. Can your program have
What do the < > more than one .c file?
mean?
This is a comment. The compiler ignores this.
#include <stdio.h>
The main() function is always
/* The simplest C Program */ where your program starts
int main(int argc, char **argv) running.
{
Blocks of code (“lexical
printf(“Hello Worldn”);
scopes”) are marked by { … }
return 0;
}
Return ‘0’ from this function Print out a message. ‘n’ means “new line”.
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10. Comment Statements
● Formal Comments:
/* Comment ….. */
● Used for detailed description of functions or
operations (for our benefit, not compiler’s).
● Can take multiple lines in source file.
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11. Pre-Processor Directives
#include -- header files for library functions
Example:
#include <stdio.h>
Note Space
#define -- define constants and macros
Examples:
#define e 2.7182818
#define pi 3.14159265359
Note Spaces
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12. Declarations
● Declarations tell the compiler what variable
names will be used and what type of data
each can handle (store).
● Example declarations:
int a, b, c ;
float r, p, q ;
double x, y, z ;
char m, n ;
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