C language basics 1

History:

 C language was developed at AT & T's Bell laboratories of USA in 1972. It is designed and written by Dennis Ritchie.

Features of C language:
1.Middle level language
2.Structural
3.Easy to understand
4.Portability i.e., programs written in one system can be copied into another system and can be executed easily
4.More efficient
5.Compile language
6.Windows, Linux and Unix are written in C because of its high performance

Compiler: basically the system understands only machine level language i.e., written in 1's and 0's.
Here compiler does the job of converting the source code to machine level language


Constant:
1. A constant is an entity that doesn't change
2.Alphabets, numbers and special symbols can be used to form constants.

                                                       constants    -  Integer constants -     5, 12, 28, 264, 768 etc

                                                                               Real constants    -      5.20, 6.25, 235.12, 5.21 etc

                                                                              Character constants- 'a', 'h', '9', '=' etc

Variable:
   A variable is an entity that does change.

Ex:        #include<stdio.h>
              #include<conio.h>
              int main()
 {
              int x=10;                  
              printf("the value of x is %d\n",x);
               x=x+1;
              printf("the value of x is %d\n",x);
 getch();
 return 0;
}

output: the value of x is 10
             the value of x is 20

Here x is a variable and 10, 20 are integer constants.

Variable types:
 1. Integer                                  - keyword is int         ex: int a, int x
 2.Real or floating point type    - keyword is float      ex: float area, float average, etc
 3.Character                               - keyword is char      ex: char a, char i, etc

Keywords:
     These are the words whose meaning has already been explained to the c compiler.
By using keywords we can construct the meaningfull statements.

           Ex: break, int, float, char, if, for.....etc
Note: keywords cannot be used as variable names.

Basic programs:

// to print hello

#include<stdio.h>
#include<conio.h>
int main()
{
printf("hello");
getch();
return 0;
}


Description:
#  - Pre processor directive:  it is a program that processes our source code before it is passed to the compiler

In the C Programming Language, the Standard Library Functions are divided into several header files.
The following is a list of functions found within the <stdio.h> header file:

FORMATTED INPUT/OUTPUT FUNCTIONS

fprintf                               Formatted File Write      
fscanf                               Formatted File Read
printf                                Formatted Write
scanf                         Formatted read
sprintf                        Formatted string write
sscanf                       Formatted string read
vfprintf                       Formatted File Write Using Variable Argument List
vprintf                        Formatted Write Using Variable Argument List
vsprintf                      Formatted String Write Using Variable Argument List  

FCLOSE	CLOSE FILE
FFLUSH	FLUSH FILE BUFFER
FOPEN	OPEN FILE
FREOPEN	REOPEN FILE
REMOVE	REMOVE FILE
RENAME	RENAME FILE
SETBUF	SET BUFFER (OBSOLETE)
SETVBUF	SET BUFFER
TMPFILE	CREATE TEMPORARY FILE
TMPNAM	GENERATE TEMPORARY FILE NAME

CHARACTER INPUT/OUTPUT FUNCTIONS

fgetc	Read Character from File
fgets	Read String from File
fputc	Write Character to File
fputs	Write String to File
getc	Read Characters from File
getchar	Read Character
gets	Read String
putc	Write Character to File
putchar	Write Character
puts	Write String
ungetc	Unread Character

BLOCK INPUT/OUTPUT FUNCTIONS

fread                          Read Block from File fwrite                          Write Block to File FILE POSITIONING FUNCTIONS fgetpos  Get File Position fseek                          File Seek fsetpos Set File Position ftell Determine File Position rewind Rewind File

conio.h library functions

---

      All C inbuilt functions which are declared in conio.h header file are given below. 

List of inbuilt C functions in conio.h file:

S.no	Function	Description
1	clrscr()	This function is used to clear the output screen.
2	getch()	It reads character from keyboard
3	getche()	It reads character from keyboard and echoes to o/p screen
4	textcolor()	This function is used to change the text color
5	textbackground()	This function is used to change text background

       

     
main()  
{
     /*main() is a function . A function is nothing but a set of statements.In a C program there can be multiple functions.All statements that belong to main() are enclosed within a pair of braces {} as shown here.*/




}



printf(" enter x value");    :  standard function used to print something on to the screen.
scanf("%d",&x);                :reads values or data from the user through input devices.
getch();                                 :It reads character from keyboard.


void main()   : does not expect any output value at the end of the program
int main()      :expects some integer value at the end of the program


//program to calculate simple interest

#include<stdio.h>
#include<conio.h>
int main()
{
int p,n;
float r,si;
p=1000;
n=3;
r=8.5;
//formula for simple interest 
si=(p*n*r)/100;
printf("%f\n",si);
return 0;
}

output: 255.000000




//To calculate simple interest for any values of p, n and r

#include<stdio.h>
#include<conio.h>
int main()
{
int p,n;
float r,si;
printf("enter values of p, n,r");
scanf("%d %d %f",&p,&n,&r);
si=(p*n*r)/100;
printf("%f",si);
return 0;
}


output: enter values of p, n,r 4 5 2
               0.400000