c-利用结构体存放信息并排序

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
struct student
{
        int id;
        char *pname;
        int score;
}*pstd;
int main()
{
        int i,j,k,m;
        char name[20];
        struct student stu[5];
        struct student tmp;
        pstd=(struct student *)malloc(sizeof(struct student));
        if(pstd==NULL){
                printf("%s\n","failed");
        }else{
        for(i=0;i<5;i++){
                scanf("%d",&stu[i].id);
                scanf("%s",name);
                stu[i].pname=(char *)malloc(20*sizeof(char));
                strcpy(stu[i].pname,name);
                scanf("%d",&stu[i].score);
                }
        }
        printf("%s\n%d\n",stu[2].pname,stu[4].score);
        tmp.pname=(char *)malloc(20*sizeof(char));
        for(j=0;j<4;j++){
                for(k=0;k<5-j-1;k++){
                        if(stu[k].score>stu[k+1].score){
                                tmp=stu[k];
                                stu[k]=stu[k+1];
                                stu[k+1]=tmp;
                        }
                }
        }
        for(m=0;m<5;m++){
                printf("%s%d\n",stu[m].pname,stu[m].score);
                free(stu[m].pname);
        }
        free(pstd);
        return 0;
}