目的：（用于对各个学生的分数从小到大排列）键盘输入学生的个数 n，通过3个函数分别对n个学生的成绩进行输入，排列，输出。
下面是程序代码，请各位看看问题出在哪里。

# include <stdio.h>
# include <malloc.h>

struct Student
{
    int age;
    float score;
    char name[100];
};

//输入函数；

void Input(void)
{
    int i, len;
    struct Student * pArr;
    //char name[100];
    //float score;
    pArr = (struct Student *)malloc(len * sizeof (struct Student));
    for(i=0; i<len; i++)
    {
        printf("请输入第%d个学生的信息：\n", i);
        
        printf("age=");
        scanf("%d", &pArr[i].age);

        printf("score=");
        scanf("%f", &pArr[i].score);

        printf("name=");
        scanf("%s", pArr[i].name);
    }
}

//输出函数

void Output()
{
    int i, len;
    struct Student * pArr;
    //char name[100];
    //float score;
    pArr = (struct Student *)malloc(len * sizeof (struct Student));
    for(i=0; i<len; i++)
    {
        printf("第%d个学生的信息是：\n", i);
        
        printf("age = %d", pArr[i].age);
        printf("score = %f", pArr[i].score);
        printf("name = %s", pArr[i].name);        
    }
}

void change()
{
    int i, j, len, age;
    struct Student * pArr;
    struct Student t;
    char name[100];
    float score;
   
    for(i=0; i<len-1; i++)
    {
        for(j=0; j<len-1-i; j++)
        {
            if(pArr[j].score>pArr[j+1].score)
            {
                t = pArr[j];
                pArr[j] = pArr[j+1];
                pArr[j+1] = t;
            
            }
        }
    }
}


int main(void)
{
    int i, len;
    struct Student * pArr;
    pArr = (struct Student *)malloc(len * sizeof (struct Student));
    printf("请输入学生的个数:\n");
    printf("len = ");
    scanf("%d", &len);

    void Input(void);
    void change();
    void Output();
   

    return 0;
}

今天才看到这个帖子，首先：

void Input(void);
    void change();
    void Output();

这个是函数声明不是函数调用。
还有程序中出现很多不必要的代码，不知楼主对变量的作用域了解多少。
这是我改动后的程序：

# include <stdio.h>
# include <malloc.h>

struct Student
{
    int age;
    float score;
    char name[100];
};
int len;  //声明为全局变量
struct Student * pArr;

//输入函数；

void Input()
{
    int i;
    //struct Student * pArr;
    //char name[100];
    //float score;
    pArr = (struct Student *)malloc(len * sizeof (struct Student));
    for(i=0; i<len; i++)
    {
        printf("请输入第%d个学生的信息：\n", i);
       
        printf("age=");
        scanf("%d", &pArr[i].age);

        printf("score=");
        scanf("%f", &pArr[i].score);

        printf("name=");
        scanf("%s", pArr[i].name);
    }
}

//输出函数

void Output()
{
    int i;
   
    //char name[100];
    //float score;
    //pArr = (struct Student *)malloc(len * sizeof (struct Student));
    for(i=0; i<len; i++)
    {
        printf("第%d个学生的信息是：\n", i);
       
        printf("age = %d", pArr[i].age);
        printf("score = %f", pArr[i].score);
        printf("name = %s", pArr[i].name);       
    }
}

void change()
{
    int i, j,age;
    struct Student t;
    //char name[100];
    //float score;
   
    for(i=0; i<len-1; i++)
    {
        for(j=0; j<len-1-i; j++)
        {
            if(pArr[j].score>pArr[j+1].score)
            {
                t = pArr[j];
                pArr[j] = pArr[j+1];
                pArr[j+1] = t;
           
            }
        }
    }
}


int main(void)
{
    int i;
    //struct Student * pArr;
   // pArr = (struct Student *)malloc(len * sizeof (struct Student));
    printf("请输入学生的个数:\n");
    printf("len = ");
    scanf("%d", &len);
    Input();
    change();
    Output();
    

    return 0;
} 

运行后：

如图。
如有不对请高手指教

没分