Character device is a device from which data is read or written as a stream of bytes i.e as a stream of bytes.

Examples : Serial ports, Consoles etc

Block device as the name suggests is a device from which data is read or written as blocks, or chunk of data at once. Normally a block would be of 4096 bytes.

Examples: Hard drives on the system.

The performance of a block driver is important as it involves movement of data from the physical memory to the virtual memory (hard disk) whenever there is a process switch. Where as performance of a character driver does not affect the performance of the system much.

crw–w–w-  1 root    root    1,   7          2011-08-17   18:54    full

here c specifes it as a char device
and

b———  1 root    root         2,  68      2011-08-17   8:54     fd0u830

b would specify a block device.

And in the above 1 which is bold is the major number and 7 is the minor number. which specify that the device using a driver with major number one and the minor number of the device is 7. similarly for the second one 2  is the major number and 68 is the minor number.

As every person has a surname/family name and the normal name for their identification. Device drivers also need to be identified and these are done using the Major number (family name) and minor number (normal name).

The major number specifies which driver to use and if you have more devices connected to the system using the same driver, those are distinguished using the minor numbers.

We can get them allocated using the following calls
These are present in <linux/kdev_t.h>

Macro that return major number is  MAJOR(dev_t dev);
and minor number is MINOR(dev_t dev);

From the above the kernel will allocate the major and minor number to the dev_t structure

If you want to give a specific  major and minor numbers and need to turn them into a dev_t, then the following macro has to be called MKDEV(int major, int minor);

Before getting into Interrupt request queue (IRQ), let us understand interrupts. Interrupts are a mechanism using which you will ask the processor to do a particular task.

These are mechanisms that the processor cannot ignore and whenever a interrupt comes, the processor will move the present working process and has to handle the interrupt. For handling the interrupt for a particular device, we need to register the interrupt handler. There are a limited number of interrupt lines available and hence you would need to request the processor to allocate a interrupt line for your device. So you request for a interrupt and the interrupt line that is requested is called an interrupt request queue.

For getting an IRQ there are APIs given in <linux/interrupt.h>

int request_irq(unsigned int irq,
irqreturn_t (*handler)(int, void *, struct pt_regs *),unsigned long flags,const char *dev_name,
void *dev_id);
void free_irq(unsigned int irq, void *dev_id);

From above it can be seen that
irq  is the interrupt number that you are requesting for.

Handler is a function pointer to the function that is to be called when an interrupt occurs.

Flags are

SA_INTERRUPT
When set, this indicates a “fast” interrupt handler. Fast handlers are executed
with interrupts disabled on the current processor

SA_SHIRQ
This bit signals that the interrupt can be shared between devices.

SA_SAMPLE_RANDOM
This bit indicates that the generated interrupts can contribute to the entropy pool used by /dev/random and /dev/urandom.

The retrun value of the request_irq function call is ’0′ if the the interrupt line with the number asked in the ‘irq’ parameter is allocated, else a negative error code is returned.

There are kernel defined functions which the user can use to request the kernel to give the available interrupts before going ahead to request one, like unsigned long probe_irq_on(void);

The memory that is obtained using vmalloc is not that efficient to work as with the memory allocated when kmalloc is used.

The memory that is set aside for the vmalloc in some architectures is less when compared to kmalloc and hence if you try to allocate more memory it might fail.

Vmalloc allocates memory by building the page tables that is tweaking them rather than directly using.

i.e the memory allocated by vmalloc is contiguous as far as the user understands but it could be memory pages fetched from different physical memory locations and a page table built on top of it.

So the overhead on vmalloc is high as it not only has to fetch the free pages but also build the page tables for the same.

So the only point where vmalloc should be used is when you need very large memory like the one during the module creation, when the code and data copied is large and a continuous memory allocation is not possible.

void *kmalloc(size_t size, int flags);

flags can be

GFP_USER
GFP_KERNEL
The above two flags can put the process to sleep
GFP_NOFS
GFP_NOIO
the above two flags will disable the file and input output systems
GFP_ATOMIC
the process cannot be put to sleep. i.e if memory is not available the allocation fails

The user gives the inputs and the device driver helps the device to understand the input given by the user and act on it.

So device drivers are way for the user to interact with the hardware connected.

Formula of area of trapezium:
Area = (1/2) * (a + b) * h

#include<stdio.h>

int main(){

float b1,b2,h;
float area;

printf("Enter the size of two bases and height of the trapezium : ");
scanf("%f%f%f",&b1,&b2,&h);

area = 0.5 * ( b1 + b2 ) * h ;

printf("Area of trapezium is: %.3f",area);

return 0;
}

Output:

Enter the size of two bases and height of the trapezium: 5 8 3
Area of trapezium is: 19.500

Formula of area of triangle:
Area = length * width

#include<stdio.h>
int main(){
float l,w;
float area;
printf("Enter size of each sides of the rectangle : ");
scanf("%f%f",&l,&w);
area = l * w;
printf("Area of rectangle is: %.3f",area);
return 0;
}

Output:

Enter size of each sides of the rectangle: 5.2 20
Area of rectangle is: 104.000

Formula of area of right angled triangle:
Area = (1/2) * height * width

#include<stdio.h>

int main(){

float h,w;
float area;

printf("Enter height and width of the right angled triangle : ");
scanf("%f%f",&amp;amp;amp;h,&amp;amp;amp;w);

area = 0.5 * h * w;

printf("Area of right angled triangle is: %.3f",area);

return 0;
}

Output:

Enter height and width of the right angled triangle: 10 5
Area of right angled triangle is: 25.000

Formula of area of equilateral triangle:
Area = (√3)/4 * a2

#include<stdio.h>
#include<math.h>

int main(){

float a;
float area;

printf("Enter size of side of the equilateral triangle : ");
scanf("%f",&a);

area = sqrt(3)/4*(a*a);

printf("Area of equilateral triangle is: %.3f",area);

return 0;
}

Output:

Enter size of side of the equilateral triangle: 5
Area of equilateral triangle is: 10.825

Formula for area of any triangle:

Area = √(s*(s-a)*(s-b)*(s-c))
Where s = (a + b + c)/2

#include<stdio.h>
#include<math.h>

int main(){

float a,b,c;
float s,area;

printf("Enter size of each sides of triangle");
scanf("%f%f%f",&amp;amp;a,&amp;amp;b,&amp;amp;c);

s = (a+b+c)/2;
area = sqrt(s*(s-a)*(s-b)*(s-c));

printf("Area of triangle is: %.3f",area);

return 0;
}

Output:

Enter size of each sides of the triangle: 2 4 5
Area of triangle is: 3.800

#include <stdio.h>
#define PI 3.141
int main(){
float r, a;
printf("Radius: ");
scanf("%f", &amp;r);
a = PI * r * r;
printf("%f\n", a);
return 0;
}

Mathematical formula for area of circle

Area = Pie*radius*radius

Here Pie is constant which is equal to

Pie = 22/7  or

3.1415926535897932384626…

 #include<stdio.h>
int main(){

int a[10],i,n,m,c,l,u;

printf("Enter the size of an array: ");
scanf("%d",&n);

printf("Enter the elements of the array: " );
for(i=0;i<n;i++){
scanf("%d",&a[i]);
}

printf("Enter the number to be search: ");
scanf("%d",&m);

l=0,u=n-1;
c=binary(a,n,m,l,u);
if(c==0)
printf("Number is not found.");
else
printf("Number is found.");

return 0;
}

int binary(int a[],int n,int m,int l,int u){

int mid,c=0;

if(l<=u){
mid=(l+u)/2;
if(m==a[mid]){
c=1;
}
else if(m<a[mid]){
return binary(a,n,m,l,mid-1);
}
else
return binary(a,n,m,mid+1,u);
}
else
return c;
}

Output:

Enter the size of an array: 5
Enter the elements of the array: 8 9 10 11 12
Enter the number to be search: 8
Number is found.

Write a c program to search an element in an array using binary search

#include<stdio.h>
int main(){

int a[10],i,n,m,c=0,l,u,mid;

printf("Enter the size of an array: ");
scanf("%d",&n);

printf("Enter the elements in ascending order: ");
for(i=0;i<n;i++){
scanf("%d",&a[i]);
}

printf("Enter the number to be search: ");
scanf("%d",&m);

l=0,u=n-1;
while(l<=u){
mid=(l+u)/2;
if(m==a[mid]){
c=1;
break;
}
else if(m<a[mid]){
u=mid-1;
}
else
l=mid+1;
}
if(c==0)
printf("The number is not found.");
else
printf("The number is found.");

return 0;
}

Output:

Enter the size of an array: 5
Enter the elements in ascending order: 4 7 8 11 21
Enter the number to be search: 11
The number is found.

Write a c program to search an element in an array using linear search

#include<stdio.h>
int main(){

int a[10],i,n,m,c=0;

printf("Enter the size of an array: ");
scanf("%d",&amp;n);

printf("Enter the elements of the array: ");
for(i=0;i<=n-1;i++){
scanf("%d",&amp;a[i]);
}

printf("Enter the number to be search: ");
scanf("%d",&amp;m);
for(i=0;i<=n-1;i++){
if(a[i]==m){
c=1;
break;
}
}
if(c==0)
printf("The number is not in the list");
else
printf("The number is found");

return 0;
}

Output:

Enter the size of an array: 5
Enter the elements of the array: 4 6 8 0 3
Enter the number to be search: 0
The number is found

#include <stdio.h>

void shellsort(int A[],int max)
{
int stop,swap,limit,temp,k;
int x=(int)(max/2)-1;
while(x>0)
{
stop=0;
limit=max-x;
while(stop==0)
{
swap=0;

for(k=0; kA[k+x])
{
temp=A[k];
A[k]=A[k+x];
A[k+x]=temp;
swap=k;
}
}
limit=swap-x;
if(swap==0)
stop=1;
}
x=(int)(x/2);
}
}
int main()
{

int i,ELEMENTS,X[100];
printf("Enter the number of elements to be sorted:");
scanf("%d",&ELEMENTS);
printf("Enter the elements to be sorted:\n");
for(i = 0; i < ELEMENTS; i++ ){
scanf("%d",&X[i]);
}
printf("Unsorted Array:\n");
for(i=0;i < ELEMENTS;i++)
printf("%d ",X[i]);

shellsort(X,ELEMENTS);
printf("\nSORTED ARRAY\n");
for(i=0;i < ELEMENTS;i++)
printf("%d ",X[i]);

printf("\n");
}

Output:

Enter the number of elements to be sorted: 5
Enter the elements to be sorted: 2 6 4 1 2
Unsorted Array: 2 6 4 1 2
SORTED ARRAY 2 1 4 2 6

#include <stdio.h>
#include <malloc.h>

void main()
{
int *x,i,n;
int temp;
void heap(int *,int);

fflush(stdin);
printf("Heap Sort");
printf("Enter How many Numbers : ");
scanf("%d",&n);
x = (int *)malloc(n * sizeof(int));
printf("Enter the elements into the array :");
for(i=0;i=1;i--)
{
temp =  x[i];
x[i] = x[0];
x[0] = temp;
heap(x,i-1);
}

printf("The array after sorting is \n");
for(i=0;i=0;i--)
{
if(a[(2*i)+1] < a[(2*i)+2] && (2*i+1)<=n && (2*i+2)<=n)
{
temp = a[(2*i)+1];
a[(2*i)+1] = a[(2*i)+2];
a[(2*i)+2] = temp;
}
if(a[(2*i)+1] > a[i] && (2*i+1)<=n && i<=n)
{
temp = a[(2*i)+1];
a[(2*i)+1] = a[i];
a[i] = temp;
}
}
}

Output:

Heap Sort Enter How many Numbers : 5
Enter the elements into the array : 2 5 0 9 1
The array after sorting is 0 1 2 5 9

#include<stdio.h>
#define MAX 50

void mergeSort(int arr[],int low,int mid,int high);
void partition(int arr[],int low,int high);

int main(){

int merge[MAX],i,n;

printf("Enter the total number of elements: ");
scanf("%d",&n);

printf("Enter the elements which to be sort: ");
for(i=0;i<n;i++){
scanf("%d",&merge[i]);
}

partition(merge,0,n-1);

printf("After merge sorting elements are: ");
for(i=0;i<n;i++){
printf("%d ",merge[i]);
}

return 0;
}

void partition(int arr[],int low,int high){

int mid;

if(low<high){
mid=(low+high)/2;
partition(arr,low,mid);
partition(arr,mid+1,high);
mergeSort(arr,low,mid,high);
}
}

void mergeSort(int arr[],int low,int mid,int high){

int i,m,k,l,temp[MAX];

l=low;
i=low;
m=mid+1;

while((l<=mid)&&(m<=high)){

if(arr[l]<=arr[m]){
temp[i]=arr[l];
l++;
}
else{
temp[i]=arr[m];
m++;
}
i++;
}

if(l>mid){
for(k=m;k<=high;k++){
temp[i]=arr[k];
i++;
}
}
else{
for(k=l;k<=mid;k++){
temp[i]=arr[k];
i++;
}
}

for(k=low;k<=high;k++){
arr[k]=temp[k];
}
}

Output:

Enter the total number of elements: 5
Enter the elements which to be sort: 2 5 0 9 1
After merge sorting elements are: 0 1 2 5 9

#include<stdio.h>

void quicksort(int [10],int,int);

int main(){
int x[20],size,i;

printf("Enter size of the array: ");
scanf("%d",&amp;size);

printf("Enter %d elements: ",size);
for(i=0;i<size;i++)
scanf("%d",&amp;x[i]);

quicksort(x,0,size-1);

printf("Sorted elements: ");
for(i=0;i<size;i++)
printf(" %d",x[i]);

return 0;
}

void quicksort(int x[10],int first,int last){
int pivot,j,temp,i;

if(first<last){
pivot=first;
i=first;
j=last;

while(i<j){
while(x[i]<=x[pivot]&amp;&amp;i<last)
i++;
while(x[j]>x[pivot])
j--;
if(i<j){
temp=x[i];
x[i]=x[j];
x[j]=temp;
}
}

temp=x[pivot];
x[pivot]=x[j];
x[j]=temp;
quicksort(x,first,j-1);
quicksort(x,j+1,last);

}
}

Output:

Enter size of the array: 5
Enter 5 elements: 3 8 0 1 2
Sorted elements: 0 1 2 3 8