平均值未正确计算

Question

I have designed a small program to calculate the average test scores for an array of students, however, for the life of me, cannot figure out why the average is not calculating properly. What is going on?

Output:

Enter number of students in class (max 50): 3 Enter total number of tests (max 10): 3 Enter student 1's test scores: 100 100 100 Enter student 2's test scores: 100 97 75 Enter student 3's test scores: 56 45 67 (lldb) (lldb) (lldb)

The average score for student 1 is 33.3333. // As you see here it should be 100 since all 3 scores were 100. (lldb)

Code:

const int MAX_STUDENTS = 50;
const int MAX_TESTS = 10;

int main()
{
    char studentName[50];
    int totalStudents = 0;
    int totalTests = 0;
    double totalScore = 0;
    double score[MAX_STUDENTS][MAX_TESTS];
    double averages[MAX_STUDENTS];

    std::cout << "Enter number of students in class (max " << MAX_STUDENTS << "): ";
    std::cin >> totalStudents;
    std::cout << "Enter total number of tests (max " << MAX_TESTS << "): ";
    std::cin >> totalTests;
    for (int student = 0; student < totalStudents; student++) {
        std::cout << "Enter student " << (student + 1) << "'s test scores: " << endl;
        for (int test = 0; test < totalTests; test++) {
            std::cin >> score[student][test];
        }
    }

    for (int student = 0; student < totalStudents; student++) {
        for (int test = 0; test < totalTests; test++) {
            totalScore = NULL;
            totalScore += score[student][test];
        }
        averages[student] = totalScore / totalTests;
        std::cout << endl;
        std::cout << "The average score for student " << student + 1 << " is " << averages[student] << "." << endl;
    }

    return 0;
}

Answer 1

Change

    for (int test = 0; test < totalTests; test++) {
        totalScore = NULL;
        totalScore += score[student][test];
    }

to

    totalScore = 0;
    for (int test = 0; test < totalTests; test++) {
        totalScore += score[student][test];
    }

Otherwise you are resetting the totalScore prior to each addition.

Answer 2

You always set totalScore to 0 inside the inner loop.

   for (int student = 0; student < totalStudents; student++) {
        for (int test = 0; test < totalTests; test++) {
            totalScore = NULL;
            totalScore += score[student][test];
        }

Statement

            totalScore = 0.0; // why NULL?

must be placed before the inner loop.

Also I would separate the calculation of average scores and printing the result.

So I would write the following way

for ( int student = 0; student < totalStudents; student++ ) 
{
    averages[student] = 0.0;
    for ( int test = 0; test < totalTests; test++ ) 
    {
        averages[student] += score[student][test];
    }
    averages[student] /= totalTests;
}

for ( int student = 0; student < totalStudents; student++ ) 
{
    std::cout << "The average score for student " << student + 1 << " is " << averages[student] << "." << endl;
}