PYTHON PROGRAMMING (23UCSCC01) – UNIT - III

History of C language

C programming language was developed in 1972 by Dennis Ritchie at bell laboratories of AT&T (American Telephone & Telegraph), located in the U.S.A.

Dennis Ritchie is known as the founder of the C language.

It was developed to overcome the problems of previous languages such as B, BCPL, etc.

 

Features of C Language

C is the widely used language. It provides many features that are given below.

1. Simple
2. Machine Independent or Portable
3. Mid-level programming language
4. structured programming language
5. Rich Library
6. Memory Management
7. Fast Speed
8. Pointers
9. Recursion
10. Extensible

1) Simple

            C is a simple language in the sense that it provides a structured approach (to break the problem into parts), the rich set of library functions, data types, etc.

2) Machine Independent or Portable

            Unlike assembly language, c programs can be executed on different machines with some machine specific changes. Therefore, C is a machine independent language.

3) Mid-level programming language

            Although, C is intended to do low-level programming. It is used to develop system applications such as kernel, driver, etc. It also supports the features of a high-level language. That is why it is known as mid-level language.

4) Structured programming language

            C is a structured programming language in the sense that we can break the program into parts using functions. So, it is easy to understand and modify. Functions also provide code reusability.

5) Rich Library

            C provides a lot of inbuilt functions that make the development fast.

6) Memory Management

            It supports the feature of dynamic memory allocation. In C language, we can free the allocated memory at any time by calling the free() function.

7) Speed

            The compilation and execution time of C language is fast since there are lesser inbuilt functions and hence the lesser overhead.

8) Pointer

            C provides the feature of pointers. We can directly interact with the memory by using the pointers. We can use pointers for memory, structures, functions, array, etc.

9) Recursion

            In C, we can call the function within the function. It provides code reusability for every function. Recursion enables us to use the approach of backtracking.

10) Extensible

            C language is extensible because it can easily adopt new features.

 

Tokens in C

            Tokens are the smallest individual unit in C. For `example, we cannot create a sentence without using words; similarly, we cannot create a program in C without using tokens in C. tokens in C is the building block or the basic component for creating a program in C language

.Classification of tokens in C

·         Keywords

·         Identifiers

·         Constants

·         Strings

·         Special Symbols

·         Operators

 

Keywords

A keyword can be defined as the pre-defined or the reserved words. It cannot be used it as a variable name, constant name, etc. There are only 32 reserved words (keywords) in the C language.

A list of 32 keywords in the c language is given below:

auto	break	case	char	const	continue	default	do
double	else	enum	extern	float	for	goto	if
int	long	register	return	short	signed	sizeof	static
struct	switch	typedef	union	unsigned	void	volatile	while

Identifiers in C

Identifiers are used for naming variables, functions, arrays, structures, etc. Identifiers in C are the user-defined words.

Rules for constructing identifiers in C are given below:

Ø  The first character should be either an alphabet or an underscore

Ø  It should not begin with any numerical digit.

Ø  In identifiers, both uppercase and lowercase letters are distinct. Therefore, we can say that identifiers are case sensitive.

Ø  No special characters are allowed except underscore.

Ø  Keywords cannot be represented as an identifier.

Ø  The length of the identifiers should not be more than 31 characters.

Constants

A constant is a fixed value or variable that can't be changed in the program, for example: 10, 20, 'a', 3.4, "c programming" etc.

There are different types of constants in C programming.

Constant	Example
Decimal Constant	10, 20, 450 etc.
Real or Floating-point Constant	10.3, 20.2, 450.6 etc.
Octal Constant	021, 033, 046 etc.
Hexadecimal Constant	0x2a, 0x7b, 0xaa etc.
Character Constant	'a', 'b', 'x' etc.
String Constant	"c", "c program", "c in javatpoint" etc.

 

Two ways to define constant in C

There are two ways to define constant in C programming.

1. const keyword
2. #define preprocessor

1) C const keyword

The const keyword is used to define constant in C programming.

Ø  const float PI=3.14;  

Now, the value of PI variable can't be changed.

#include<stdio.h>    

int main()

{    

 const float PI=3.14;    

printf("The value of PI is: %f",PI);    

 return 0;  

}     

Output:

The value of PI is: 3.140000

 

#include<stdio.h>    

int main()

{    

const float PI=3.14;     

PI=4.5;    

printf("The value of PI is: %f",PI);    

   return 0;  

}     

Output:

Compile Time Error: Cannot modify a const object

 

2) C #define preprocessor ( Symbolic Constant )

            Symbolic constant is name that substitute for a sequence of character that cannot be changed. The character may represent a numeric constant, a character constant, or a string. When the program is compiled, each occurrence of a symbolic constant is replaced by its corresponding character sequence. They are usually defined at the beginning of the program.

The #define preprocessor is also used to define constant.

#include<stdio.h> 

#define a=10;

#define pi=3.14;   

int main()

{    

pi=5.5;

printf("The value of PI is: %f",PI);    

 return 0;  

}     

Strings in C

            -are always represented as an array of characters having null character '\0' at the end of the string. This null character denotes the end of the string. Strings in C are enclosed within double quotes, while characters are enclosed within single characters. The size of a string is a number of characters that the string contains.

Now, we describe the strings in different ways:

char a[10] = "javatpoint"; // The compiler allocates the 10 bytes to the 'a' array.

har a[] = "javatpoint"; // The compiler allocates the memory at the run time.

char a[10] = {'j','a','v','a','t','p','o','i','n','t','\0'}; // String is represented in the form of characters.

Operators in C

            -is a special symbol used to perform the functions. The data items on which the operators are applied are known as operands. Operators are applied between the operands. Depending on the number of operands, operators are classified as follows:

            Unary Operator

            A unary operator is an operator applied to the single operand. For example: Positive sign (+), negative sign (-), increment operator (++), decrement operator (--), sizeof, (type)*.

            Binary Operator

            `The binary operator is an operator applied between two operands. The following is the list of the binary operators:

• Arithmetic Operators
• Relational Operators
• Shift Operators
• Logical Operators
• Bitwise Operators
• Conditional Operators
• Assignment Operator
• Misc Operator

Special characters in C

Some special characters are used in C, and they have a special meaning which cannot be used for another purpose.

• Square brackets [ ]: The opening and closing brackets represent the single and multidimensional subscripts.
• Simple brackets ( ): It is used in function declaration and function calling. For example, printf() is a pre-defined function.
• Curly braces { }: It is used in the opening and closing of the code. It is used in the opening and closing of the loops.
• Comma (,): It is used for separating for more than one statement and for example, separating function parameters in a function call, separating the variable when printing the value of more than one variable using a single printf statement.
• Hash/pre-processor (#): It is used for pre-processor directive. It basically denotes that we are using the header file.
• Asterisk (*): This symbol is used to represent pointers and also used as an operator for multiplication.
• Tilde (~): It is used as a destructor to free memory.
• Period (.): It is used to access a member of a structure or a union.

 

Variables in C

            A variable is a name of the memory location. It is used to store data. Its value can be changed, and it can be reused many times. It is a way to represent memory location through symbol so that it can be easily identified.

Syntax

            datatype variable_list;  

 

Eg:

int a;  

float b;  

char c; 

int a=10,b=20;//declaring 2 variable of integer type  

float f=20.8;  

char c='A';

 

Here, a, b, c are variables. The int, float, char are the data types.

Assigning values to the variable

            Values can be assigned to variables using the assignment operator = as follows.

Syntax

            Variable_name=constant;

Eg:

            ini_valu=0;

            balance=75.64;

            Yes=’x’;

Rules for defining variables

• A variable can have alphabets, digits, and underscore.
• A variable name can start with the alphabet, and underscore only. It can't start with a digit.
• No whitespace is allowed within the variable name.
• A variable name must not be any reserved word or keyword, e.g. int, float, etc.

Valid variable names:

int a;  

int _ab;  

int a30;  

Invalid variable names:

int 2;  

int a b;  

int long;