Introduction about Low Level Programming using C

LOW LEVEL PROGRAMMING
Register Variables

Register variables are stored in CPU register instead of memory.

Frequently used variables are kept in registers and they have faster
accessibility.

They are local to the function

Example
#include <stdio.h>
void main() {
register char x = 'S';
register int a = 10;
int b = 8;
printf("The value of register variable : %c",x);
printf("The sum is: %d",(a+b));
}
O/P:
The value of register variable : S
The sum is: 18

Bitwise Operations
 To perform bit-level operations in C programming, bitwise
operators are used.
 When we perform the bitwise operations, then it is also known as
bit-level programming.
 It consists of two digits, either 0 or 1.

#include <stdio.h>
void main()
{
int a = 5, b = 9;
printf("a = %d, b = %dn", a, b);
printf("a&b = %dn", a & b);
printf("a|b = %dn", a | b);
printf("a^b = %dn", a ^ b);
printf("~a = %dn", a = ~a);
printf("b<<1 = %dn", b << 1);
printf("b>>1 = %dn", b >> 1);
}

Bit Fields
 struct
{ data - type[nameofmember]: width_of_Bit - field; };
struct example1
{
int val1;
int val2;
};
struct example2
{
int val1: 1;
int val2: 1;
};
void main()
{
printf(“ Size of memory engaged by example_bitField : %u ", sizeof(struct example1));
printf(“ Size of memory engaged by example_bitField2: %u ", sizeof(example2));
}
Output:
Size of memory engaged by example1 : 8
Size of memory engaged by example2 : 4

ADDITIONAL FEATURES OF C
Enumerations
 Enumeration (or enum) is a user defined data type in C.
 An enum is a special type that represents a group of constants
(unchangeable values).
 To create an enum, use the enum keyword.
 Example
enum week{Mon, Tue, Wed, Thur, Fri, Sat, Sun};
void main()
{
enum week day;
day = Wed;
printf("%d",day);
}
O/P
 2

Command Line Parameters
 The arguments passed from command line are called
command line arguments.
 These arguments are handled by main() function.
 The structure of main() function as given below.
int main(int argc, char *argv[] )
 Here, argc counts the number of arguments.
It counts the file name as the first argument.
 The argv[] contains the total number of arguments. The first
argument is the file name always.

#include <stdio.h>
int main( int argc, char *argv[] )
{
printf("Program name %sn", argv[0]);
if( argc == 2 )
{
printf("The argument supplied is %sn", argv[1]);
}
else if( argc > 2 )
{
printf("Too many arguments supplied.n");
}
}

STRINGS
Defining a String
 A string is a collection of characters (i.e.,
letters, numerals, symbols, and punctuation
marks) in a linear sequence.
 A String in C is an array with character as a
data type.
 The syntax of declaring a string in C is:
char variable[array_size];
 Ex.
char str[5];
char str2[50];

NULL Character
 Strings are actually one-dimensional array of characters
terminated by a null character '0'.
 Ex.
char arr[6] = {'H', 'e', 'l', 'l', 'o', '0'};
 You can write the above statement as follows −
char arr[] = "Hello";
#include <stdio.h>
void main ()
{
char arr[6] = {'H', 'e', 'l', 'l', 'o', '0'};
printf("%s", arr );
}

Initialization of Strings
1. Assigning a string literal without size
 String literals can be assigned without size.
char str[] = “Jhon";
2. Assigning a string literal with a predefined size
 String literals can be assigned with a predefined size.
 If we want to store a string of size n then we should always declare a
string with a size equal to or greater than n+1.
char str[5] = " Jhon";
3. Assigning character by character with size
 We can also assign a string character by character.
 But we should remember to set the end character as ‘0’ which is a null
character.
char str[5] = { ‘J’,‘h’,‘o’,‘n’,'0'};
4. Assigning character by character without size
 We can assign character by character without size with the NULL
character at the end.
 The size of the string is determined by the compiler automatically.
char str[] = { ‘J’,‘h’,‘o’,‘n’,'0'};

Reading and Writing a String
scanf() and printf() functions
#include<stdio.h>
void main()
{
char str[50];
printf("Enter the string? ");
scanf("%s",str);
printf("%s",str);
}
gets() and puts() functions
#include<stdio.h>
void main ()
{
char s[30];
printf("Enter the string? ");
gets(s);
puts(s);
}

Processing a String
#include <stdio.h>
#include <stdlib.h>
void main()
{
char str[100];
int l= 0;
printf("Find the length of a string :n");
printf("Input the string : ");
scanf(“%s”,str);
while(str[l]!='0')
{
l++;
}
printf("Length of the string is : %d", l-1);
}

Searching and Sorting of Strings
String Functions:

Sorting
#include <stdio.h>
#include <string.h>
void main ()
{
char string[] = “efacbd";
char temp;
int i, j;
int n = strlen(string);
printf("String before sorting - %s n", string);
for (i = 0; i < n-1; i++) {
for (j = i+1; j < n; j++) {
if (string[i] > string[j]) {
temp = string[i];
string[i] = string[j];
string[j] = temp;
} } }
printf("String after sorting - %s n", string);
}

Searching
#include <string.h>
void main()
{
char s[100],c;
int i;
printf("Enter the string : ");
gets(s);
printf("Enter character to be searched: ");
c=getchar();
for(i=0;s[i];i++)
{
if(s[i]==c)
{
printf("character '%c' found at location: %dn ",c,i);
}
}
}

Introduction about Low Level Programming using C

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