1、赋值地方，应该是a[i][j],这里i、j代表第几个，你用student这些固定值，一看就知道错了不是吗？而且这是个非常严重的错误，a[i][j]这里面i不能等于student，j不能等于subiects，你们下标取值0到student-1，你自己写完看看都知道错了

2、sum每次循环前要赋0，否则会把前一个学生的成绩加进去

3、ave=sum*1.0/4，不乘1.0的话，系统会把sum/4当成一个整型，会造成结果不正确

#include

#define subiects 3 //学科数量

#define students 4 //学生人数

int main(void)

{

int a[students][subiects] = { 53,54,76,87,89,56,76,85,45,75,76,45 };

int i = 0, j = 0, sum = 0;//sum为总分

double ave;//ave为平均值

//输入成绩

for (i = 0; i < students; i++)

{

printf("请输入学生%d的%d科成绩:", i + 1, subiects);//i+1为学生序号

for (j = 0; j < subiects; j++)

{

scanf("%d", &a[i][j]);//students=4,subiects=3,你觉得a[4][3]赋值是赋给谁？下面同样错误

}

}

//输出成绩

printf("\t\tC语言\t大英\t高数\t总分\t平均分\n");

for (i = 0; i < students; i++)

{

sum=0;//每次都要赋0，否则会把前面同学成绩加进去

printf("\t同学%d", i+1);

for (j = 0; j < subiects; j++)

{

sum += a[i][j];//错误

printf("\t%d", a[i][j]);//错误

}

ave = sum*1.0 / subiects;

printf("\t%d\t%.2f\n",sum,ave);

}

printf("\n\n");

//颠倒输出

sum = 0;

ave = 0;

printf("\t");

for (i = 0; i < students; i++)

printf("\t同学%d", i + 1);

printf("\t平均分\n");

for (j = 0; j < subiects; j++)

{

if (j == 0)

printf("\tC语言");

if (j == 1)

printf("\t大英");

if (j == 2)

printf("\t高数");

sum=0;//赋0

for (i = 0; i < students; i++)

{

sum += a[i][j];//错误

printf("\t%d", a[i][j]);//错误

}

ave = sum*1.0 / students;

printf("\t%.2f\n",ave);

}

return 0;

}