我需要遵守并获得结果的代码。//wap输入2个学生的分数并打印每个学生的平均分数;

#include<stdio.h>//foramte of c programming
void avg(arr[][],int a);//defined the function to calculate the average marks
int main(){//formate
   int marks[2][3];//defcalration of the arras with the space to be occpied
   for(int i=0;i<2;i++)//for the input of the numbers
   {
    printf("Enter the three subject marks of %d students:",i+1);
    for(int j=0;j<3;j++)
    {
        scanf("%d",marks[i][j]);
    } 
   }//end of the input
   int avg1=avg(marks,0);
   printf("The average marks of the 1st student is %d",avg1);
   int avg2=avg(marks,1);
   printf("The average marks of the 2nd student is %d",avg2);
   return 0;
}
void  avg(arr[][],int a)//function definition
{
    for( int i=a;i<a+1;i++)
    {
        for(int j=0;j<3;j++)
        {
            sum=sum+marks[i][j];
        }
        
    }
     int average=sum/3;
     return average;//return the average marks of the arra that is declared
}

在编译代码时，我得到了很多错误：错误也粘贴在这里：

averageof2students.c:3:10: error: unknown type name 'arr'
 void avg(arr[][],int a);//defined the function to calculate the average marks
          ^~~
averageof2students.c: In function 'main':
averageof2students.c:14:13: warning: implicit declaration of function 'avg' [-Wimplicit-function-declaration]
    int avg1=avg(marks,0);
             ^~~
averageof2students.c: At top level:
averageof2students.c:20:11: error: unknown type name 'arr'
 void  avg(arr[][],int a)//function definition`

请帮助我得到想要的结果。我是编程世界的初学者

从上面的结果我想要的结果的平均成绩的2名学生的3个不同的科目分数使用数组和函数的概念。我已经遵循了DSA（数据结构算法），但在完成时，我去了错误信息。请帮我解决这个问题。我在网上和书上搜索，但无法找到答案。