QuickSort/快速排序/快排

#include <stdio.h>
#include <time.h>
#include <getopt.h>
#include <stdlib.h>

void exchange(int *array,int i1,int i2)
{
        int temp;
        temp=array[i1];
        array[i1]=array[i2];
        array[i2]=temp;
}

int partition(int *array,int begin,int end)
{
        int pivot_index;
        int pivot;
        int i,j;
        srand(time(NULL));
        pivot_index=rand()%(end-begin+1)+begin;
        exchange(array,pivot_index,end);
        pivot_index=end;
        pivot=array[pivot_index];
        j=begin-1;
        for(i=begin;i<end;i++)
        {
                if(array[i]<pivot)
                {
                        j++;
                        exchange(array,i,j);
                }
        }
        exchange(array,j+1,pivot_index);
        return j+1;
}

void quicksort(int *array,int begin,int end)
{
        int pa;
        if(begin<end)
        {
                pa=partition(array,begin,end);
                quicksort(array,begin,pa-1);
                quicksort(array,pa+1,end);
        }
}

int main(int argc,char *argv[])
{
        int op;
        int num;
        int i;
        FILE *fp_input=stdin;
        FILE *fp_output=stdout;
        int *array;
        while((op=getopt(argc,argv,":i:o:"))!=-1)
        {
                switch(op)
                {
                        case 'i':
                                fp_input=fopen(optarg,"r");
                                if (fp_input==NULL)
                                {
                                        fprintf(stderr,"open file %s fail!",optarg);
                                        return 1;
                                }
                                break;
                        case 'o':
                                fp_output=fopen(optarg,"w");
                                if(fp_output==NULL)
                                {
                                        fprintf(stderr,"open file %s fail!!",optarg);
                                        return 1;
                                }
                                break;
                        case ':':
                                fprintf(stderr,"option needs a value\n");
                                break;
                        case '?':
                                fprintf(stderr,"unknow option: %c\n",optopt);
                                break;

                }
        }
        fscanf(fp_input,"%d",&num);
        array=(int *)malloc(num*sizeof(int));
        if (array==NULL)
        {
                fprintf(stderr,"out of space!!!\n");
                return 2;
        }

        for(i=0;i<num;i++)
        {
                fscanf(fp_input,"%d",array+i);
        }

        quicksort(array,0,num-1);

        for(i=0;i<num;i++)
        {
                fprintf(fp_output,"%d",*(array+i));
        }
        fprintf(fp_output,"\n");
        free(array);
        fclose(fp_input);
        fclose(fp_output);
        return 0;
}