需要帮助do-while循环程序？ （C ++）

Question

我正在尝试创建一个程序，它将获取用户输入（标记）并将这些标记的平均值输出到字母等级。 我相信我已经成功地让计划成功地计算平均值，但它不会输出正确的字母等级？

有什么建议吗？ 编辑：也许它是计算中的东西，因为我的输出总是给出百分比作为“F”等级....

// Used iomanip to display averages for possible three digit or greater answers.
#include <iostream>
#include <iomanip>
using namespace std;

// Set up my program using only main()
int main()
{
    //Created the variable 'mark' so the user input can be stored and tested in the do-while condition.
    //Variable 'sum' and 'average' to calculate mark and then be tested against letter grades.
    //'counter' used to keep track of number of terms being averaged.
    double mark=0, sum=0, average=0;
    int counter=-1;

    // Do-while statement to test the loop. Gets input from user, and tests whether it is a a valid letter grade.
    // Marks below 0 or above 100 will test true and loop back re-promting the user for another mark.
    // If tested condition is false, then if statements then test the mark and output the letter grade.

    cout << "Please enter marks to calculate average, and enter -1 to stop and find letter equivalence. " << endl;

    do
    {
        if ( mark < 0 || mark > 100 )
        {
            cout << "Entered mark is invalid. Please try again, or enter -1 to stop and find letter equivalence. " << endl;
            break;
        }

        sum = sum + mark;
        counter++;
        cin >> mark;

    }
    while ( mark != -1 );

    average = sum / counter ;

    //What happens when above statement is false...
    if (mark >= 90)
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of A+ ";
        }
    else if (mark >=80)
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of A ";
        }
    else if (mark >=70)
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of B ";
        }
    else if (mark >=60)
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of C ";
        }
    else if (mark >=50)
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of D ";
        }
    else
        {
            cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of F ";
        }
return 0;
}

Answer 1

要考虑的事情：

1. 您的成绩分配应考虑average而非marks。如果您使用标记，那么最后输入的值-1将退出您的do while循环将用于评分，这将始终导致F等级。

2. 在endl循环后，将cout添加到您的所有do-while语句中。输出流可能已被缓冲，这可能导致cout语句不显示在您的监视器上。 endl将刷新输出流。

例如。
cout << "The average of "<<setprecision(2)<<average<<"% is equivalent to a letter grade of A+ " << endl;

Answer 2

仔细检查if语句。我打赌你总是看到正确的平均值等于F。

Answer 3

在循环结束时，mark始终为-1。因此，所有测试都失败了，您将进入else子句，并输出F.修复是测试average，而不是mark。