array.....

i want to write a rogram to display the student gpa first enter the score show the average of the gpa,highest and lowest
the display total the number of grade in 2 dimensional array
i stuck in the middle don't know how to calculate the gpa realy stuck in thia part
this is my program

Code:

#include<stdio.h>
#include<stdlib.h>
#define column_size 30
#define row_size 50

void input_table(int *rows,int *column,int arr[][column_size]);
void output_table(int rows,int columns,const int arr[][column_size]);

int main()
{

	int test_score[row_size][column_size];
	int rows,columns,score;
	
	input_table(&rows,&columns,test_score);
	output_table(rows,columns,test_score);

	return 0;
}
void input_table(int *no_of_rows,int *no_of_columns,int arr[][column_size])
{
	int i,j;
                printf("\n");
	printf("\t\t\UNIVERSITY OF SUNDERLAND\n");
	printf("\t\t\t------------------------\n");
	printf("\n");
  	printf("Enter number of rows    : ");
	scanf("%d",&(*no_of_rows));
	printf("Enter number of columns : ");
	scanf("%d",&(*no_of_columns));

	for(i=1;i<=*no_of_rows;i++)
		for(j=1;j<=*no_of_columns;j++)
		{
			printf("Enter value of test score [%d][%d] :",i,j);
	     	scanf("%d",&arr[i][j]);
		
		}
}
void output_table(int rows,int columns,const int arr[][column_size])
{    
	int i,j;
	
                system("cls");
	printf("\n");
	printf("\t\t\tEXAMINATION PERFORMANCE REPORT\n");
	printf("\t\t\t------------------------------\n");
	printf("\n");
                printf("Student No\tAACS1089\tAACS1283\tGrade Point Average\n");
	printf("-------------\t--------\t--------\t-------------------\n");

	for(i=1;i<=rows;i++){
		printf("\t\n%3d",i);
	for(j=1;j<=columns;j++)
		printf("\t\t%3d",arr[i][j]);
	}
	
	printf("\n\n");
	printf("AVERAGE GPA = %d\n ");
	printf("\n");
	printf("HIGHEST GPA =  %d     obtained by student No.=\n");
	printf("LOWEST  GPA =  %d     obtained by student No.=\n");
   
	}