使用多个如果C++ else语句

Question

我没有编程经验，我正在一类称为介绍C++工程师。我们目前正在学习如何使用else语句，并且为什么我的程序没有正确执行以及我犯了什么错误，我一直坚持了几天。

我需要创建一个计算并显示一个任期内采取两班的GPA的程序。我还没有学习循环，所以我需要硬编码两个类的计算和输入。问题是，当我为两个类输入任何等级信件时，它总是将第一个if语句视为在两种情况下都是真实的。

#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这一点，但现在我刚学的基础知识，所以我将不胜感激保持相关课程的范围答案。

谢谢！

编辑：我想这可能是必要提及的是我的理解是双不需要的变量。在节目结束时，我也不需要操纵或任何cout。我只是想弄清楚出了什么问题。 :-)

Answer 1

那是因为你正在使用的赋值操作符，“=”，而不是运营商相比，“==”，在你的if语句。所以你没有比较Grade，你正在分配它。

有几种方法来减少这类问题。一种是尽可能地将变量声明为'const';这会将不需要的分配标记为错误。另一种方法是反转if语句中的变量和字面值（即if（'A'== Grade）），它具有相同的效果。

另外，如果你打开所有的编译器警告，你可能只得到这样的警告，以及。当然，这取决于你的编译器。