Sắp xếp trộn

#include<conio.h>
#include<stdio.h>
#include<time.h>
#include<stdlib.h>
int a[1000],n0,k_dem=1;
int ran(int a1, int a2)
{
    return rand()%(a2-a1+1)+a1;
}

int inmang(int a[], int n)
{
    int i;
    for (i=1;i<=n;i++)
        printf("%d ",a[i]);
    return 0;
}
int merge(int first, int mid, int last)
{
    int m[1000],n[1000],i=1,j=1,k,i0,j0;
    for (k=first;k<=mid;k++)
        m[i++]=a[k];
    for (k=mid+1;k<=last;k++)
        n[j++]=a[k];
    i0=i; j0=j; i=1; j=1;
    for (k=first;k<=last;k++)
    {
        if (j==j0 || m[i]<=n[j] && i!=i0) a[k]=m[i++];
        else if (i==i0 || m[i]>n[j]) a[k]=n[j++];
    }
    printf("\nStep %2d, conquer %2d-%2d, %2d-%2d: ",k_dem++,first,mid,mid+1,last); inmang(a,n0);
    return 0;
}

int merge_sort(int first, int last)
{
    int mid;
    if (first<last)
    {
        mid=(first+last)/2;
        printf("\nStep %2d, divide: %2d-%2d, %2d-%2d: ",k_dem++,first,mid,mid+1,last);
        inmang(a,n0);
        merge_sort(first,mid);
        merge_sort(mid+1,last);
        merge(first,mid,last);
    }
    return 0;
}

int main()
{
    int a1,a2,i;
    srand((unsigned)(time(NULL)));
    printf("Nhap vao so phan tu: "); scanf("%d",&n0);
    printf("Nhap vao gia tri dau: "); scanf("%d",&a1);
    printf("Nhap vao gia tri cuoi: "); scanf("%d",&a2);
    for (i=1;i<=n0;i++)
        a[i]=ran(a1,a2);
    printf("Mot mang da duoc tao ngau nhien ra la: \n"); inmang(a,n0);
    merge_sort(1,n0);
    printf("\n\nMang sau khi duoc sap xep la: \n"); inmang(a,n0);
    getch();
    return 0;

}