How to find the average of the two sets of data?

The average of the first data set should be: (80+70+65+89+90)/5 and the second set (85+80+80+82+87)/5, but for some reason my code is not working.

When I run the code I get 17.0 and 219886384 instead of 78.8 and 82.8.

int main(void)
{
    int grades[2][5] = {{80, 70, 65, 89, 90}, {85, 80, 80, 82, 87}};
    float average;
    int sum;
    int i;
    int j;
    for(i = 0; i < 2; i++)
    {
        sum = 0;
        for(j = 0; j < 5; j++);
        {
            sum += grades[i][j];
        }
        average = sum / 5;
        printf("The average grade for %d is: %f\n", i, average);
    }
    return 0;
}


A ';' means the finish of the for loop so your code 'for(j = 0; j < 5; j++);' equals to j=5;

Array Index Out Of Bounds!