algorithm - merge sort using recursion in c languaage -

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#include<stdio.h> #include<conio.h> int arr[20];        void main() {     int n,i;     clrscr();     printf("\n\t\t\t------merge sorting------\n\n");     printf("enter size of array\n");     scanf("%d",&n);     printf("enter elements:\n");     for(i=0; < n; i++)     {         scanf("%d",&arr[i]);     }     merge_sort(arr,0,n-1);     printf("\n\n\t\t\t-----merge sorted elements-----\n\n");     printf("sorted array:\t");     for(i=0; < n; i++)     {         printf("\t%d",arr[i]);     }     getch(); }  int merge_sort(int arr[],int low,int high) {     int mid;     if(low < high)     {         mid=(low+high)/2;         merge_sort(arr,low,mid);         merge_sort(arr,mid+1,high);         merge(arr,low,mid,high);     } } int merge(int arr[],int l,int m,int h) {     int arr1[10],arr2[10];     int n1,n2,i,j,k;     n1=m-l+1;     n2=h-m;     for(i=0; <  n1; i++)     {         arr1[i]=arr[l+i];     }     for(j=0; j < n2; j++)     {         arr2[j]=arr[m+j+1];     }     arr1[i]=9999;     arr2[j]=9999;     i=0;     j=0;     for(k=l; k <=h; k++)     {         if(arr1[i]<=arr2[j])             arr[k]=arr1[i++];         else             arr[k]=arr2[j++];     } }

if in program taking input array of size 7.so main() merge_sort(arr,0,6) passed respective function after condition checked if(0<6) there mid becomes 3 ,then there recursive call low = 0 , mid = 3,then time mid 1 again recursive call with(arr,0,1) ..and on till low , mid equals 0 ,then there if condition fails because if(0<0) not true

but , able understand how merge_sort(arr,mid+1,high); being called?but program runs fine .please explain how compiler calling merge_sort(arr,mid+1,high)

based on comments, real question is: given bit of recursive code:

int merge_sort(int arr[],int low,int high) {     int mid;     if(low < high)     {         mid=(low+high)/2;         merge_sort(arr,low,mid);         merge_sort(arr,mid+1,high);   // 1         merge(arr,low,mid,high);     } }

how can indicated line ever reached, since line before recurses same function?

within conditional block, value of mid first set value between low , high points. mid becomes high next iteration, bringing low , high closer together. if(low < high) fail, terminating leg of recursion.


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