C语言 结构体 动态数组：程序改错

要求：对动态数组中n个学生的数据，按成绩升序实现选择排序。

#include<stdio.h>
#include<stdlib.h>
struct student
{
    int id;
    char name[20];
    float score;
};
struct student *input(int n);
void sort(struct student *pstu,int n);
void output(struct student stu[],int n);
void swap(struct studdent *p1,struct studdent *p2);

int main()
{
    struct student *pstu;
    int n;
    printf("请输入学生人数：");
    scanf("%d",&n);
    printf("请输入学生学号、姓名、成绩：");
    pstu=input(n);
    sort(pstu,n);
    output(pstu,n);
    free(pstu);
    return 0;
}

//输入
struct student *input(int n)
{
    int i;
    struct student *pstu=(struct student *)calloc(n,sizeof(struct student));
    for(i=0;i<n;i++)
        scanf("%d %s %f",&pstu[i].id,pstu[i].name,&pstu[i].score);
    return pstu;
}
//排序
void sort(struct student *pstu,int n)
{
    struct student *pmin,*p;
    int i;
    for(i=0;i<n-1;i++)
    {
        pmin=pstu+i;
        for(p=pmin+1;p<pstu+n;p++)
            if(p->score < pmin->score)
                  pmin=p;
        if(pmin!=pstu+i)
            swap(pmin,pstu+i);
    }
}
//交换
void swap(struct studdent *p1,struct studdent *p2)
{
    struct student tmp;
    tmp = p1;
    p1 = p2;
    p2 = tmp;
}
//输出
void output(struct student *pstu,int n)
{
    struct student *p;
    p=pstu;
    while(p<pstu+n)
    {
        printf("%d %s %f",p->id,p->name,p->score);
        p++;
    }
}

//交换
void swap(struct studdent *p1,struct studdent *p2)
{
   struct student tmp;
   tmp = *p1;
   *p1 = *p2;
   *p2 = tmp;
}