꼭 함수로 써야할 이유가 있다면 모를까..
이것 보다도 더 쉬운 소스가 있습니다.


#include<stdio.h>

char hak(int a[]);

main()
{

    char num[10][9], name[20][10], result[20][10];
    int kor[10][9], eng[10][9], mat[10][9],i,j;
    float ave[10][9];

    for(i=0; i<3; i++)
//       for(j=0 ; j<1 ; j++)
       {
    {
        printf("Input the number :");
        scanf("%s", num[i]);
    printf("The number is %s\n", num[i]);


        printf("\nInput the name:");
        scanf("%s", name[i]);
    printf("%s's name is %s\n", num[i],name[i]);


    printf("\nInput the korean score :");
        scanf("%d", &kor[i]);
        result[20][10]= hak(kor[i]);
//    printf("%s", kor[i]);


    printf("\nInput the engilsh score:");
        scanf("%d", &eng[i]);
        result[20][10]= hak(eng[i]);
//        printf("%d",eng[i]);


    printf("\nInput the math score:");
        scanf("%d", &mat[i]);
    result[20][10]= hak(mat[i]);
//    printf("%s\n\n", mat[i]);

        }
    }


//    for(j=0; j<3; j++)
        {
//            printf("%s %s %d %d %d\n", num[j], name[j], kor[j], eng[j], mat[j]);
//            printf("%c", result);
                        
    }
        return 0;

}

char hak(int a[])
{
    int i;
    char num[10][9];
    for(i=0;i<=0 ;i++ )
        {
    if(a[i]>100 || a[i]<0)
            printf("ERROR\n");
        else if(a[i]<=100 && a[i]>=90)
        printf("grade is A\n");
        else if(a[i]>=80)
        printf("grade is B\n");
        else if(a[i]>=70)
        printf("grade is C\n");
    else if(a[i]>=60)
        printf("grade is D\n");
        else if(a[i]<=59)
        printf("grade is F\n");
        }

return 0;
}