Tech-Notes

C

Developed at AT&T bell laboratories in 1972 by Dennis Ritchie.

FIRST PROGRAM:

#include<stdio.h>		//preprocessor command which tell compiler to include stdio.h file   
int main(){				//c program starts from main function  
	printf("Hello world!");
	return 0;			//will return 0 for os
}

KEYWORDS:(44 keywords)

auto,break,case,char,const,Continue,default,do,Double,extern,Float,for,goto,If,Inline,Int,long,register,short,Signed,sizeof,static,Struct,switch,typedef,union,unsigned

VARIABLES:

  1. global- which is defines outer main function
  2. local - inside main function

Variable_types:

  1. Primary:
    1. Integeral- int (1byte), char (2byte)
    2. Floating- float (4byte), double (8byte)
  2. Secondary:
    1. Signed char (1 byte) -128 to 127 %c
    2. Unsigned char(1 byte) 0 to 255 %c
    3. Short signed int (2 byte) -32,768 to 32,768 %d
    4. Short unsigned int(2 byte) 0 to 65535 %u
    5. Signed int (2 byte) -32,768 to 32,768 %d
    6. Unsigned int (2 byte) 0 to 65535 %u
    7. Long signed int (4 byte) -2,147,483,648 to 2,147,483,648 %Ld
    8. Long unsigned int (4 byte) 0 to 4294967295 %lu
    9. Float(4 byte) -3.4e38 to 3.4e38 %f
    10. Double(8 byte) -1.7e308 to -1.7e308 %lf
    11. Long double(10 byte) -1.7e4938 to 1.7e4932 %lf

*float value=4e10 //4 power10
*sizeof(value)// it will print bytes occupied by value
*null character // ’\0’
Typedef: rename a datatype, syntax: typedef int rajesh; rajesh a=10;//rajesh become int

OPERATORS:

  1. Arithmetic operators +-*/%
  2. Relational operators <, <=,>,>=, ==,! =,Take !a>=400 as a<=400.
  3. Logical operators &&(and),||(or),!(not) is for bytes
  4. Assignment operators x+=y is x=x+y
  5. Increment decrement operators ++,–
  6. Conditional operators(ternary) condition?exp1:exp2;
  7. Bitwise operators &(and),|(or),^(xor),~(1s compliment), <<(left),>>(rigth)
  8. Special operators comma, sizeof, pointer, member selection
  9. Typecasting z=x(float)/y(float) where x and y is int

FLOW CONTROL:

  1. if
  2. if ..else
  3. if ..else if
  4. switch(i){case 1:printf(1); default:printf(“default”);}

LOOPS:

  1. while
  2. do..while
  3. for(int i=0;i<n;i++)
  4. goto error; error: printf(“error”);
  5. break;
  6. continue;

INPUT OUTPUT:

  1. formatted - scanf(); printf(); fscan(); fprint();
  2. unformatted - getc(variable);getchar(variable);gets(variable); putc(variable); putchar(variable) puts(variable);

Conditional statements

  1. %c character
  2. %d integer
  3. %s string
  4. %f float
  5. %p pointer

ARRAY:

collection of similar datatype

int a[5]; int a[]={1,2,3,4,5};
a) one dimensional, b) two dimensional, c) three dimensional

STRING:

array of character

char name[] = "rajesh";
char name[5] = {"r","a","j","e","s","h"}

POINTER:

variable contains address of another variable

int *a; a=&b;  a=0;//null pointer or default  
*a=55; printf("%d",&b);//55  
printf("%d",*a);

address type will be whole number(2 byte)
pointer’s subraction allowed but other math operation not allowed in c

FUNCTION:

set of instruction that are used to perform specified tasks

int getName(int arg){
	return 3;
}
  1. arg pass by reference - func(&a); int func(int *arg){….}
  2. arg pass by value

STRUCTURE:

storing different datatype in one variable

struct student{
	int rollno;
	char name[];
}
struct student rajesh = {1,"rajesh"};

UNION:

same like strucutre but memory allocation difference and takes half of struct size

union student{
	int rollno;
	char name[];
}
union student rajesh = {1,"rajesh"};

FILE HANDLING:

FILE *fpointer;
Fpointer=fopen(“rajesh.txt”,”w”); //r-read, w-write, a-edit

STANDARD LIBRARY HEADER:

  1. #include<stdio.h> - prinf,scanf,getchar,putchar
  2. #include<stdlib.h> - number rconversion, memory alloc, exit and system, quick sort
  3. #include<float.h> - system liit for flot type
  4. #include<math.h> - mathematical function
  5. #include<assert.h> - assertions
  6. #include<ctype.h> - character class tests
  7. #include<limits.h> - system limit for integral types
  8. #include<setjmp.h> - non local jumps
  9. #include<signal.h> - signal and error handling
  10. #include<stdarg.h> - variable length parameter list
  11. #include<string.h> - string function
  12. #include<time.h> - date and time functions
  13. #include<conio.h> - clrscr(), getch(), getche() etc

MEMORY ALLOCATION:

char description; description=malloc(100sizeof(char)); //now we can use description variable as
realloc(descrciption, 100*sizeof(char));