使用多個如果C++ else語句

Question

我沒有編程經驗，我正在一類稱爲介紹C++工程師。我們目前正在學習如何使用else語句，並且爲什麼我的程序沒有正確執行以及我犯了什麼錯誤，我一直堅持了幾天。

我需要創建一個計算並顯示一個任期內採取兩班的GPA的程序。我還沒有學習循環，所以我需要硬編碼兩個類的計算和輸入。問題是，當我爲兩個類輸入任何等級信件時，它總是將第一個if語句視爲在兩種情況下都是真實的。

#include <iostream> 
#include <iomanip> 

using namespace std; 

int main() 
{ 

    double gpa, qualityPoints, qualityPoints1, qualitypointsTotal, totalCredits, credits, credits1; 
    double cqPoints, cqPoints1; 
    char grade, grade1; 

    cout << "Grade Point Average Calculator" << endl << endl; 

    cout << "Enter the grade letter received for the first class: " << endl; 
    cin >> grade; 

    if (grade = 'A') 
    { 
     qualityPoints = 4.0; 
    } 
    else if (grade = 'B') 
    { 
     qualityPoints = 3.0; 
    } 
    else if (grade = 'C') 
    { 
     qualityPoints = 2.0; 
    } 
    else if (grade = 'D') 
    { 
     qualityPoints = 1.0; 
    } 

    else if (grade = 'F') 
    { 
     qualityPoints = 0.0; 
    } 

    else 
    { 
     cout << "Invalid Letter Grade" << endl; 
    } 

    cout << "How many credit hours was the class worth?" << endl; 
    cin >> credits; 

    cqPoints = qualityPoints * credits; 

    cout << "Enter the grade letter received for the second class: " << endl; 
    cin >> grade1; 

    if (grade1 = 'A') 
    { 
     qualityPoints1 = 4.0; 
    } 
    else if (grade1 = 'B') 
    { 
     qualityPoints1 = 3.0; 
    } 
    else if (grade1 = 'C') 
    { 
     qualityPoints1 = 2.0; 
    } 
    else if (grade1 = 'D') 
    { 
     qualityPoints1 = 1.0; 
    } 
    else if (grade1 = 'F') 
    { 
     qualityPoints1 = 0.0; 
    } 

    else 
    { 
     cout << "Invalid Letter Grade" << endl; 
    } 
    cout << "How many credit hours was the class worth?" << endl; 
    cin >> credits1; 

    cqPoints1 = qualityPoints1 * credits1; 

    totalCredits = credits + credits1; 

    cout << "Total credit hours earned this term: " << totalCredits << endl; 

    qualitypointsTotal = cqPoints + cqPoints1; 

    gpa = qualitypointsTotal/totalCredits; 

    cout << "Your GPA for this term is: " << gpa << endl; 


    cout << "Credits: " << credits << endl; 
    cout << "Credits1: " << credits1 << endl; 
    cout << "qualityPoints: " << qualityPoints << endl; 
    cout << "qualityPoints1: " << qualityPoints1 << endl; 
    cout << "cqPoints: " << cqPoints << endl; 
    cout << "cqPoints1: " << cqPoints1 << endl; 
    cout << "qualitypointsTotal: " << qualitypointsTotal << endl; 
    cout << "totalCredits: " << totalCredits << endl; 
    return 0; 

} 

我很清楚，有更有效的方法可以做到這一點，但現在我剛學的基礎知識，所以我將不勝感激保持相關課程的範圍答案。

謝謝！

編輯：我想這可能是必要提及的是我的理解是雙不需要的變量。在節目結束時，我也不需要操縱或任何cout。我只是想弄清楚出了什麼問題。 :-)

Answer 1

那是因爲你正在使用的賦值操作符，「=」，而不是運營商相比，「==」，在你的if語句。所以你沒有比較Grade，你正在分配它。

有幾種方法來減少這類問題。一種是儘可能地將變量聲明爲'const';這會將不需要的分配標記爲錯誤。另一種方法是反轉if語句中的變量和字面值（即if（'A'== Grade）），它具有相同的效果。

另外，如果你打開所有的編譯器警告，你可能只得到這樣的警告，以及。當然，這取決於你的編譯器。