[counting sort] bản hoàn chỉnh

#include<stdio.h>
#include<stdlib.h>
#define MAX 10000
#define in "in.txt"
#define out "out.txt"
int findmax(int a[], int n)
{
    int max = a[0];
    for (int i = 1; i < n; ++i)
    {
        if(a[i]>max)
            max = a[i];
    }
    return max;
}
void print_array(int a[],int n)
{
       for ( int i = 0; i < n; i++ )
                        printf( "%d ",a[i]);
           printf( "\n");
}
void insertionsort(int a[], int n)
{
        int i,j,key;
        for (int j = 1; j < n; ++j)
        {
                key = a[j];
                i = j -1;
                while(i>=0&&a[i]>key)
                {
                        a[i+1] = a[i];
                        i = i-1;
                }
                a[i+1] = key;
        }
}
void countingsort(int a[],int b[], int k)
{
    //int c[MAX];
    int *c;
    c = (int*)malloc(MAX);
    for (int i = 0; i < k; ++i)
    {
        c[i] =0;
    }
    for (int i = 0; i < MAX; ++i)
    {
        c[a[i]] = c[a[i]] + 1;
    }
    for (int i = 1; i < k; ++i)
    {
        c[i]= c[i] + c[i-1];
    }
    for (int i = MAX-1; i >= 0; --i)
    {
        b[c[a[i]]-1] = a[i];
        c[a[i]] = c[a[i]] -1;
        //print_array(a,11);
        //print_array(b,11);
    }
    free(c);
}
void GhiFileSoNguyen(int n)
{
    FILE *f;
    f = fopen(in,"wt");
    if(f==NULL)
    {
        printf("Khong tao duoc file\n");
        //getch();
        exit(0);
    }
    for (int i = 0; i < n; ++i)
    {
        fprintf(f, "%d\n", rand()%1000);
    }
    fclose(f);
}
void GhiFile(int a[MAX], int n)
{
    FILE *f;
    f = fopen(out,"wt");
    if(f==NULL)
    {
        printf("Khong tao duoc file\n");
        //getch();
        exit(0);
    }
    for (int i = 0; i < n; ++i)
    {
        fprintf(f, "%d\n", a[i]);
    }
    fprintf(f, "\n" );
    fclose(f);
}
void DocFile(int a[MAX], int n)
{
    FILE *f;
    f = fopen(in,"rt");
    if(f==NULL)
    {
        printf("Khong doc duoc file\n");
        //getch();
        exit(0);
    }
    for (int i = 0; i < n; ++i)
    {
        fscanf(f, "%d", &a[i]);
    }
    fclose(f);
}
int main(int argc, char const *argv[])
{
    int a[MAX];
    int b[MAX];
    GhiFileSoNguyen(MAX);
    DocFile(a,MAX);
    countingsort(a,b,findmax(a,MAX)+1);
    GhiFile(b,MAX);
    /*for(int i=0; i<MAX; i++)
        printf("%d\n",a[i]);*/
    system("pause");
    return 0;
}