#include <stdio.h>
#define classes
void main()
{
    long sid;
    long cid;
    short credit;
    float score;
    char type;
    sid=981101;
    cid=8101;
    credit=3;
    score=89;
    type='a';
    printf("\n 你 输入的学生成绩信息\n");
    printf("班    级:%s\n",classes);
    printf("学    号:%1d\n",sid);
    printf("课程编号:%1d\n",cid);
    printf("学    分:%d\n",credit);
    printf("成    绩:%6.2f\n",score);
    printf("课程类型:%c\n",type);
}

#define classes
 printf("班    级:%s\n",classes);
你的define没写完整  

谢谢

#include <stdio.h>
#define classes 2
void main()
{
    long sid;
    long cid;
    int credit;
    float score;
    char type;
    sid=981101;
    cid=8101;
    credit=3;
    score=89;
    type='a';
    printf("\n 你 输入的学生成绩信息\n");
    printf("班    级:%d\n",classes);
    printf("学    号:%1d\n",sid);
    printf("课程编号:%1d\n",cid);
    printf("学    分:%d\n",credit);
    printf("成    绩:%6.2f\n",score);
    printf("课程类型:%c\n",type);
}