# Sort data using Quick Sort - C Program

Write a C program to create a file named as “item.txt”. Store names of ten items such as “Keyboard”, “mouse” etc. Then read those names from the same file and sort them in ascending order using quick sort. Finally print them.

Solution:

Quick sort:
Quick sort is an efficient sorting algorithm which is based on divide and conquer algorithm. In this sorting technique it picks a pivot value and divide the given array around the picked pivot.

In this example we used file to store the data and sort them in ascending order using quick sort.

#### Program

#include <stdio.h>
#include <string.h>
#define max 10
struct nick
{
char a[10];
};

void quicksort(struct nick items[], int left, int right);                   //function for quick sort

int main()
{
FILE *fp;
int i=0,k=0,n;
char fname[10],str[10],c;
struct nick name[max];
printf("Enter the filename : ");
scanf("%s",fname);
printf("\nEnter the number of products : ");
scanf("%d",&n);
printf("Enter %d product name : \n",n);
fp=fopen(fname,"w");
for(i=0;i<n;i++)
{
scanf("%s",name);
fprintf(fp,"%s ",name);
}
fclose(fp);
i=0;

fp=fopen(fname,"r");                   //open file in read mode
while((c=getc(fp))!=EOF)
{
if(c==' ')
{
str[i]='\0';
strcpy(name[k].a,str);          //copy string name to name
i=0;
k++;
}
else
{
str[i]=c;
i++;
}
}
fclose(fp);
printf("\nInitial contents of file\n");
for(i=0; i<k; i++)
printf("%s,", name[i].a);
quicksort(name,0,k-1);                              //calling quicksort
printf("\n\nAfter applying quick sort \n");
for(i=0; i<k; i++)
{
printf("%s,", name[i].a);                       //printing sorted
}
return 0;
}
//function for quick sort
void quicksort(struct nick items[],int first,int last)
{
int j,i,pivot;
char temp[10];
if(first<last)
{
pivot=first;
i=first;
j=last;
while(i<j)
{
while((strcmp(items[i].a,items[pivot].a))<0)
i++;
while((strcmp(items[j].a,items[pivot].a))>0)
j--;

if(i<j)
{
strcpy(temp,items[i].a);          //swap the values at i and j'th index
strcpy(items[i].a,items[j].a);
strcpy(items[j].a,temp);
}
}
strcpy(temp,items[pivot].a);
strcpy(items[pivot].a,items[j].a);
strcpy(items[j].a,temp);
quicksort(items,first,j-1);                 //recursive call to quick sort
quicksort(items,j+1,last);
}
}

Output: