PART-1 Over View of C language ( engineering)

DATA STRUCTURES – R19 Course Code-A5502
Part -1: Overview of C
Structure of a C program, data types, operators, type conversion,
formatted input/out functions, Control statements.
1. Structure of a C Program
1. Documentations (Documentation Section)
The Documentation section usually contains the collection of comment lines giving the name of
the program, author's or programmer's name and few other details.
Comments:
 Comments are a way of explaining what makes a program.
 The compiler ignores comments
 Comment can be used anywhere in the program to add info about the program or code block
 Used by other users /programmers to understand the code.
The comments are specified as
a) Single line comment
E.g.: // Program to find factorial
b) Multi line comment

E.g.: /*
Program Name is – Factorial
Author Name is – Ramesh
Outcome – Understand loop
*/
2. Preprocessor Statements (Link Section)
This instructs the compiler to connect to the various functions from the system library
3. Definition Section
The Definition section describes all the symbolic-constant.
4. Global Declarations (Definition Section)
Used to define those variables that are used globally within the entire program and is used in
more than one function. This section also declares all the user-defined functions.
5. The main() function
All C programs must have a main () which contains two parts:
Declaration part: Used to declare all variables that will be used within the program. In C
Variables must be declared before using in the program statements.
Execution part: At least one statement for execution
 These two parts are declared within the opening and closing curly braces of the
main ().
 The execution of the program begins at the opening brace '{' and ends with the
closing brace '}'.
 All the statements of these two parts need to be terminated with a semi-colon.
6. User Defined Functions
Deals with all user-defined functions that are called from the main ()
User-defined functions are declared and usually defined after the main () function.
Every C program must consist of one or more functions
Every function has one or more statements to perform a task.
Every C program must have function main (), the execution of a C program begins with
this function. It is an entry point for a C Program.

2. Data types in C
C language is rich in its data types.
The Data type determines
The type of value a data item can have.
The range of values a data item can take.
The size of data item in memory bytes.
Possible Operations performed on the data.
C- Supports four modifiers for data types
1. signed - For Positive and Negative Value
2. unsigned - For positive only
3. short - size specifier
4. long - size specifier

The Primitive/Primary/ Basic data types in C are
1. char: It stores a single character and requires a single byte of memory in almost all compilers.
o C – Language uses ASCII character set.
o Characters are stored in their ASCII codes (American Standard Code for Information
Interchange).
o ASCII Character set uses 128 characters from 0-127. (1 Byte)
o ASCII Value of A -> 65 , a->97 , 0 ->48
2. int: It is used to store integer value. (2 Bytes)
3. float: It is used to store floating point value with single precision. (4 Bytes)
4. double: It is used to store floating point value with double precision. (8 Bytes)
5. void: It has no value. It is used to specify the type of functions. If the function is void then it
will not return any value.
Note: The size of Data type varies from one System to another.

The basic data types and their sizes
S.No Data Type Size in Bytes Range
1 char 1 -128 to +127
2 unsigned char 1 0 to 255
3 signed char 1 -128 to +127
4 int 2 -32768 to +32767
5 unsigned int 2 0 to 65535
6 signed int 2 -32768 to +32767
7 short int 2 -32768 to +32767
8 unsigned short int 2 0 to 65535
9 signed short int 2 -32768 to +32767
10 long int 4 -2147483648 to +21474833647
11 unsigned long int 4 0 to 4294967295
12 signed long int 4 -2147483648 to +21474833647
13 float 4 3.4E-38 to 3.4E+38
14 double 8 1.7E-308 to 1.7E+308
15 long double 10 3.4E-4932 to 1.1E+4932
Identifiers in C
 Identifiers are names given to program elements such as variables, arrays, and functions.
 The name of identifier is formed with any sequence of letters (upper and lower case), numerals
and underscore (_). [Alpha numeric characters only]
Rules for forming identifiers
1. Can not include any special characters or punctuation marks except underscore. E.g. @avg,
avg#
2. Key words cannot be used as identifier names. E.g. int for;
3. Identifier must start with a letter or underscore. E.g. _avg , Avg,avg
4. Must not contain white spaces. E.g. AVG CSE
5. Identifiers are case sensitive. E.g. AVG differ from avg
6. Identifier can be of any reasonable length (only first 31 characters are significant). E.g. Average

Keywords in C
Keywords are the reserved words and have a specific meaning already defined by the compiler.
Keywords are a sequence of characters.
Key words are the building blocks for writing C programs.
All keywords must be written in lower case.
Keywords cannot be used as identifier names.
The meaning of a keyword cannot be changed.
The list of keywords supported in C are
Variables and Constants in C
Variables: The primary purpose of variables is to store data in memory for later use. Variables value
may change during execution. If you declare a variable in C, that means you are asking to the operating
system for reserve a piece of memory with that variable name.
A variable has
 Name – Any valid identifier name
 Value - The value of specified type
 Address- The memory address where the variable stored.
 Scope – The range of statements or program, the variable is visible.
 Lifetime- How long the variable does exist in memory.

Syntax:
type variable_name;
type variable_name1, variable_name2, variable_namen;
int width, height=5; //variable declaration and initialization
char symbol='A'; //char declaration and initialization
unsigned int count;
signed short int age;
float age, area; //variable declaration
double d;
Constants: Constants is the most fundamental and essential part of the C programming language.
Constants in C are the fixed values that are used in a program, and its value remains the same during
the entire execution of the program.
 Constants are used to define fixed values.
 Values of constants can never be changed.
 Constants are also called literals.
 Constants can be any of the data types.
 It is considered best practice to define constants using only upper-case names.
 Keyword const is used to define constants.
 The constants can be integer constants, character constants, float or real constants.
Syntax:
const type constant_name;
E.g: const int MAX=20;
 const float PI=3.142;
 const double SQRT_2=1.414;
 const char GRADE=’A’;

3. Type Conversions

4. Formatted Input/Output Functions

5. Operators in C

Operator Precedence and Associativity
 Precedence Rule decides the order in which different operators are applied in an
expression.
 Associativity rule decides the order in which multiple occurrences of the same level
precedence operators are applied in an expression.

PART-1 Over View of C language ( engineering)

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