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Variables
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:type variable_list;
The example of declaring the variable is given below:
» int a;
» int _ab;
» int a30;
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:
» int a=10,b=20;//declaring 2 variable of integer type
» float f=20.8;
» 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:
» int a;» int _ab;
» int a30;
Invalid variable names:
» int 2;» int a b;
» int long;
Types of Variables in C
There are many types of variables in c:» local variable
» global variable
» static variable
» automatic variable
» external variable
1. 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.
void function1(){
int x=10;//local variable
}
You must have to initialize the local variable before it is used.
2. 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.
int value=20;//global variable
void function1(){
int x=10;//local variable
}
3. Static Variable
A variable that is declared with the static keyword is called static variable.It retains its value between multiple function calls.
void function1(){
int x=10;//local variable
static int y=10;//static variable
x=x+1;
y=y+1;
printf("%d,%d",x,y);
}
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.
4. 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.void main(){
int x=10;//local variable (also automatic)
auto int y=20;//automatic variable
}
5.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
extern int x=10;//external variable (also global)
Constants
A constant is a 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.
List of Constants in C
| 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 codesikhe" etc. |
Character Constants
Character literals are enclosed in single quotes, e.g., 'x' can be stored in a simple variable of char type.A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').
There are certain characters in C that represent special meaning when preceded by a backslash for example, newline (\n) or tab (\t).
Following is the example to show a few escape sequence characters −
#include <stdio.h>
int main()
{
printf("Hello\tWorld\n\n");
return 0;
}
When the above code is compiled and executed, it produces the following result −
Hello World
Hello World
String Literals
String literals or constants are enclosed in double quotes "". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.You can break a long line into multiple lines using string literals and separating them using white spaces.
Here are some examples of string literals. All the three forms are identical strings.
"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
Defining Constants
There are two simple ways in C to define constants −→ Using #define preprocessor.
→ Using const keyword.
The #define Preprocessor
Given below is the form to use #define preprocessor to define a constant −#define identifier value
The following example explains it in detail −
#include <stdio.h>
#define LENGTH 10
#define WIDTH 5
#define NEWLINE '\n'
int main() {
int area;
area = LENGTH * WIDTH;
printf("value of area : %d", area);
printf("%c", NEWLINE);
return 0;
}
The const Keyword
You can use const prefix to declare constants with a specific type as follows −const type variable = value;
The following example explains it in detail −
#include <stdio.h>
int main() {
const int LENGTH = 10;
const int WIDTH = 5;
const char NEWLINE = '\n';
int area;
area = LENGTH * WIDTH;
printf("value of area : %d", area);
printf("%c", NEWLINE);
return 0;
}
value of area : 50
Comments
Comments in C language are used to provide information about lines of code. It is widely used for documenting code. There are 2 types of comments in the C language.
- Single Line Comments
- Multi-Line Comments
⪼ Single Line Comments
Single line comments are represented by double slash \\. Let's see an example of a single line comment in C.
#include<stdio.h>
int main(){
//printing information
printf("Hello C");
return 0;
}
Output:
Hello C
Even you can place the comment after the statement. For example:
printf("Hello C");//printing information
⪼ Mult Line Comments
Multi-Line comments are represented by slash asterisk \* ... *\. It can occupy many lines of code, but it can't be nested. Syntax:
/*
code
to be commented
*/
Let's see an example of a multi-Line comment in C.
#include<stdio.h>
int main(){
/*printing information
Multi-Line Comment*/
printf("Hello C");
return 0;
}
Output:
Hello C
Escape Sequences
Sometimes, it is necessary to use characters that cannot be typed or has special meaning in C programming. For example: newline(enter), tab, question mark etc.
In order to use these characters, escape sequences are used.
| Escape Sequences | Character |
|---|---|
\b | Backspace |
\f | Form feed |
\n | Newline |
\r | Return |
\t | Horizontal tab |
\v | Vertical tab |
\\ | Backslash |
\' | Single quotation mark |
\" | Double quotation mark |
\? | Question mark |
\0 | Null character |
For example: \n is used for a newline. The backslash \ causes escape from the normal way the characters are handled by the compiler.
