需要“ do-while循環程序”幫助嗎？ （C ++）

Question

我正在嘗試創建一個程序，該程序將接受用戶輸入（標記）並將這些標記的平均值輸出到字母等級。 我相信我已經成功地使程序成功地計算了平均值，但是它不會輸出正確的字母等級？

有什么建議么？ 編輯：也許這是計算中的某件事，因為我的輸出始終將百分比表示為“ F”級。

// 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

需要考慮的幾件事：

1. 您的成績分配應考慮average而不是marks 。 如果使用標記，則最后一個輸入的值-1用於退出do while循環）將用於評分，這將始終導致F評分。

2. 在do-while循環之后，將endl添加到所有cout語句中。 輸出流可能已被緩沖，這可能導致cout語句未出現在監視器上。 endl將刷新輸出流。

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

Answer 2

仔細檢查您的if語句。 我敢打賭，您總是會看到正確的平均值等於F。

Answer 3

在循環結束時， mark始終為-1 。 因此，所有測試均失敗，您進入了else子句，並輸出了F。解決方法是測試average而不是mark 。