#include <stdio.h>

void letter();

int average;

int main()
{
    int a[100], i, sum = 0, num, lowest, test;

    printf("Enter the numbers of tests: ");
    scanf("%d", &test);

    while (test > 100 || test <= 0)
    {
        printf("Error! The number of tests should be in range of (1 to 100).\n");
        printf("Enter the number again: ");
        scanf("%d", &test);
    }

    for(i = 0; i < test; ++i)
    {
        printf("%d. Enter grade for this test: ", i+1);
        scanf("%d", &a[i]);
        sum += a[i];
    }

    lowest = a[0];

    for (i = 0; i < num; i++)
    {
        if (a[i] < lowest)
        {
            lowest = a[i];
        }
    }

    average = sum / test;
    printf("Average = %d\n", average);
    letter();   //added call to letter()

   return (0);
}

void letter()
{
    if (average == 0 || average <= 60)
    {
        printf("Your average is a F. \n");
    }

    else if (average <= 70 || average >= 61)
    {
        printf("Your average is a D. \n");
    }

    else if (average <= 80 || average >= 71)
    {
        printf("Your average is a C. \n");
    }

    else if (average <= 90 || average >= 81)
    {
        printf("Your average is a B. \n");
    }

    else if (average <= 100 || average >= 91)
    {
        printf("Your average is a A. \n");
    }
}