用了strcpy函数还是不行，谢谢大家的热心回应，我自己再试试

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

 
struct rating{
     int rating_2011;
     int rating_2012;
};

 
struct school{
     char name[20];
     struct rating rating;
     int school_num;
};

 
int main ()
{
    char a[20];
    int b,c,d;
    struct school no1;
    struct school no2;
    printf("plz enter your school name:\n");
    scanf("%s",a);
    printf("plz enter your school rating in 2011:\n");
    scanf("%d",&b);
    printf("plz enter your school rating in 2012:\n");
    scanf("%d",&c);
    printf("plz enter your school number:\n");
    scanf("%d",&d);
     
    strcpy(no1.name, a);
    no1.rating.rating_2011 = b;
    no1.rating.rating_2012 = c;
    no1.school_num = d;
    no2=no1;
     
    printf("the name of your school is %s\n", no1.name);
    printf("the rating of %s in 2011 is %d\n",no1.name,no1.rating.rating_2011);
    printf("the rating of %s in 2012 is %d\n",no1.name,no1.rating.rating_2012);
    printf("the school number of %s is %d\n", no1.name,no1.school_num);
     
    printf("\n");
     
    printf("the name of your school is %s\n", no2.name);
    printf("the rating of %s in 2011 is %d\n",no2.name,no2.rating.rating_2011);
    printf("the rating of %s in 2012 is %d\n",no2.name,no2.rating.rating_2012);
    printf("the school number of %s is %d\n", no2.name,no2.school_num);
     
    printf("\n");
     
    system("Pause");
    return 0;
}

plz enter your school name:
Tom
plz enter your school rating in 2011:
3
plz enter your school rating in 2012:
2
plz enter your school number:
456
the name of your school is Tom
the rating of Tom in 2011 is 3
the rating of Tom in 2012 is 2
the school number of Tom is 456

the name of your school is Tom
the rating of Tom in 2011 is 3
the rating of Tom in 2012 is 2
the school number of Tom is 456

问题解决了，太感谢beyondyf
但有一点不明白，为何把字串内容指派给结构内的成员要用strcpy函数而不可以直接no1.name=a;？？？？

你的结构中name是数组，虽然其名称相当于指针，但不能改变。你想那么做的话可以将name改成指针类型，但这样做存在安全风险，其它代码对a的改变将直接反应到name上，并且当a的生存期结束后name将成为悬空指针。一种更好的方案是用malloc从堆中动态申请内存分配给name而不是将栈内的内存分配给name。你代码中的a是栈内的一块内存。