(3) Variables in C by Apli Academy

 

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.

Let's see the syntax to declare a variable:

1. type variable_list;  

The example of declaring the variable is given below:

1. int a;  
2. float b;  
3. char c;  

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

We can also provide values while declaring the variables as given below:

1. int a=10,b=20;//declaring 2 variable of integer type  
2. float f=20.8;  
3. char c='A';  

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:

1. int a;  
2. int _ab;  
3. int a30;  

Invalid variable names:

1. int 2;  
2. int a b;  
3. int long;  

Types of Variables in C

There are many types of variables in c:

1. local variable
2. global variable
3. static variable
4. automatic variable
5. external variable

Local Variable

A variable that is declared inside the function or block is called a local variable.

It must be declared at the start of the block.

1. void function1(){  
2. int x=10;//local variable  
3. }  

You must have to initialize the local variable before it is used.

Global Variable

A variable that is declared outside the function or block is called a global variable. Any function can change the value of the global variable. It is available to all the functions.

It must be declared at the start of the block.

1. int value=20;//global variable  
2. void function1(){  
3. int x=10;//local variable  
4. }  

Static Variable

A variable that is declared with the static keyword is called static variable.

It retains its value between multiple function calls.

1. void function1(){  
2. int x=10;//local variable  
3. static int y=10;//static variable  
4. x=x+1;  
5. y=y+1;  
6. printf("%d,%d",x,y);  
7. }  

If you call this function many times, the local variable will print the same value for each function call, e.g, 11,11,11 and so on. But the static variable will print the incremented value in each function call, e.g. 11, 12, 13 and so on.

Automatic Variable

All variables in C that are declared inside the block, are automatic variables by default. We can explicitly declare an automatic variable using auto keyword.

1. void main(){  
2. int x=10;//local variable (also automatic)  
3. auto int y=20;//automatic variable  
4. }  

External Variable

We can share a variable in multiple C source files by using an external variable. To declare an external variable, you need to use extern keyword.

myfile.h

1. extern int x=10;//external variable (also global)  

program1.c

1. #include "myfile.h"  
2. #include <stdio.h>  
3. void printValue(){  
4.     printf("Global variable: %d", global_variable);  
5. }  

(2) History of C lanuage by Apli Academy

 

History of C Language

History of C language is interesting to know. Here we are going to discuss a brief history of the 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.

Initially, C language was developed to be used in UNIX operating system. It inherits many features of previous languages such as B and BCPL.

Let's see the programming languages that were developed before C language.

Language	Year	Developed By
Algol	1960	International Group
BCPL	1967	Martin Richard
B	1970	Ken Thompson
Traditional C	1972	Dennis Ritchie
K & R C	1978	Kernighan & Dennis Ritchie
ANSI C	1989	ANSI Committee
ANSI/ISO C	1990	ISO Committee
C99	1999	Standardization Committee

------------------------------------------------------------------------------------------------------------------------

Apli Academy

(1) C Programming Language Tutorial By Apli Academy

C language Tutorial with programming approach for beginners and professionals, helps you to understand the C language tutorial easily. Our C tutorial explains each topic with programs.

The C Language is developed by Dennis Ritchie for creating system applications that directly interact with the hardware devices such as drivers, kernels, etc.

C programming is considered as the base for other programming languages, that is why it is known as mother language.

It can be defined by the following ways:

1. Mother language
2. System programming language
3. Procedure-oriented programming language
4. Structured programming language
5. Mid-level programming language

1) C as a mother language

C language is considered as the mother language of all the modern programming languages because most of the compilers, JVMs, Kernels, etc. are written in C language, and most of the programming languages follow C syntax, for example, C++, Java, C#, etc.

It provides the core concepts like the array, strings, functions, file handling, etc. that are being used in many languages like C++, Java, C#, etc.

---

2) C as a system programming language

A system programming language is used to create system software. C language is a system programming language because it can be used to do low-level programming (for example driver and kernel). It is generally used to create hardware devices, OS, drivers, kernels, etc. For example, Linux kernel is written in C.

It can't be used for internet programming like Java, .Net, PHP, etc.

---

3) C as a procedural language

A procedure is known as a function, method, routine, subroutine, etc. A procedural language specifies a series of steps for the program to solve the problem.

A procedural language breaks the program into functions, data structures, etc.

C is a procedural language. In C, variables and function prototypes must be declared before being used.

---

4) C as a structured programming language

A structured programming language is a subset of the procedural language. Structure means to break a program into parts or blocks so that it may be easy to understand.

In the C language, we break the program into parts using functions. It makes the program easier to understand and modify.

---

5) C as a mid-level programming language

C is considered as a middle-level language because it supports the feature of both low-level and high-level languages. C language program is converted into assembly code, it supports pointer arithmetic (low-level), but it is machine independent (a feature of high-level).

A Low-level language is specific to one machine, i.e., machine dependent. It is machine dependent, fast to run. But it is not easy to understand.

A High-Level language is not specific to one machine, i.e., machine independent. It is easy to understand.

---

C Program

In this tutorial, all C programs are given with C compiler so that you can quickly change the C program code.

File: main.c

1. #include <stdio.h>  
2. int main() {  
3. printf("Hello C Programming\n");  
4. return 0;  
5. }  

A detailed description of above program is given in next chapters.

--------------------------------------------------------------------------------------------------------

Apli Academy