阅读3次考试.输出学生姓名、成绩、平均成绩和字母成绩.嵌套循环

Question

一切都在正常计算，除了计算平均值只适用于第一个输入(有5个学生年级输入，每个年级3个(

我只是需要帮助解释为什么它似乎只计算一年级。

示例输出：

Jake Smith-考试成绩：67 45 32，平均成绩：48.0，字母成绩：F

Jerry Jones-考试成绩：80 90 100，平均成绩：90.0，字母成绩：

Hanna Davis-考试成绩：88 78 85，平均成绩：83.66666666667，字母成绩：B

我的输出：

Jake Smith-考试成绩：67 45 32，平均成绩：48.0，字母成绩：F

Jerry Jones-考试成绩：80 90 100，平均成绩：138.0，字母成绩：

Hanna Davis-考试成绩：88 78 85，平均成绩：221.66666666666，字母成绩：

import java.util.Scanner;
public class StudentExamAvgLtrGrade {
public static void main(String[] args) {
final int ROWS = 5, COLUMNS = 3;

Scanner scnr = new Scanner(System.in);
String[] studentName = { "Jake Smith", "Jerry Jones", "Hanna Davis", "Betty Lewis", "Elle Garcia" };                    
double[] numericAverage = new double[ROWS];
char[] gpa = new char[ROWS];
int[][] studentGrade = new int[ROWS][COLUMNS];
double total;
total = 0.0;
for (int i = 0; i < ROWS; i++) {
for (int j = 0; j < COLUMNS; j++) {
studentGrade[i][j] = scnr.nextInt();
total += studentGrade[i][j];
}
numericAverage[i] = total / studentGrade[i].length; //its something about this that seems to be the issue
if(numericAverage[i] < 60) {
gpa[i] = 'F';
} else if(numericAverage[i] < 70) {
gpa[i] = 'D';
} else if(numericAverage[i] < 80) {
gpa[i] = 'C';
} else if(numericAverage[i] < 90) {
gpa[i] = 'B';
} else {
gpa[i] = 'A';
}
}

// Use nested for loops to read in the exam grades (the outside loop is your rows and inside loop is columns)
// Inside the innermost loop, keep a running total of the student's grades
// When the innermost loop completes, compute the average for that student and store it in the numericAverage array
// Hint to compute average: 
// numericAverage[i] = total / studentGrade[i].length; // i is the counter in the row loop
// Use the numericAverage value to determine the letter grade and populate the gpa array 
// Hint to compute letter grade: 
// if (numericAverage[i] < 60)  // i is the counter in the row loop
//     gpa[i] = 'F';
// else if (numericAverage[i] < 70) 
//     ...

// Use nested for loops to iterate through the arrays and output array data
// (notice the nested loop to output the exam grades stored in the 2-d array)

for (int i = 0; i < ROWS; i++)
{
System.out.print(studentName[i] + " - Exam Grades:");
for (int j = 0; j < COLUMNS; j++)
System.out.print(" " + studentGrade[i][j]);
System.out.println(", Average: " + numericAverage[i] + ", Letter Grade: " + gpa[i]);
}
}
}

Answer 1

您遇到的问题是：total = 0.0;

你在for循环之外设置总数，所以它会计算所有学生的所有成绩，所以你应该这样做：

double total;
for (int i = 0; i < ROWS; i++) {
total = 0.0;
for (int j = 0; j < COLUMNS; j++) {
...
}
...
}

Answer 2

每次计算平均值后，应将total变量重置回0。像这样：

total = 0.0;
for (int i = 0; i < ROWS; i++) {
for (int j = 0; j < COLUMNS; j++) {
studentGrade[i][j] = scnr.nextInt();
total += studentGrade[i][j];
}
numericAverage[i] = total / studentGrade[i].length; //its something about this that seems to be the issue
total = 0; //THIS!!
if(numericAverage[i] < 60) {
gpa[i] = 'F';
} else if(numericAverage[i] < 70) {
gpa[i] = 'D';
} else if(numericAverage[i] < 80) {
gpa[i] = 'C';
} else if(numericAverage[i] < 90) {
gpa[i] = 'B';
} else {
gpa[i] = 'A';
}
}