在 C++ 中将 char 转换为 int

Question

我正在编写一个 GPA 计算器程序，我想将 char 的值更改为不同的数字。

例如，如果用户输入字母 a 或 A，则值将为 4。这就是我的程序的样子。如果我使用开关盒，我知道如何使它工作，但我想这样做。

      char userInput;
      char A, a = 4;  // i want to change the value of A, a to 4
      char B, b = 3;  // i want to change the value of B, b to 3
      char C, c = 2;  // i want to change the value of C, c to 2
      char D, d = 1;  // i want to change the value of D, d to 1
      char F, f = 0;  // i want to change the value of F, f to 0
      int count2 = 0;
      int count3 = 0;
      double gpa;

// the for loop is to make sure program will only run 3 times
for (int i=1; i<4;i++)
{
  cout << "Test #" << i << ":" << endl;
  cout << endl;

  // the do while loop is being used to ensure that the user gets to
  // input at least once.
  do
  {
   cout << "Enter a Letter Grade (enter 'X' to exit): ";
   cin >> userInput;
       // the while loop is only being used for input valiation.
     while (userInput!='A' && userInput!='a' && userInput!='B' &&
            userInput!='b' && userInput!='C' && userInput!='c' &&
            userInput!='D' && userInput!='d' && userInput!='F' &&
            userInput!='f' && userInput !='X' && userInput !='x')
          {
           cout << "\n  Invalid letter grade, please try again.\n";
           cout << "\n  Enter Letter Grade (enter 'X' to exit):";
           cin >> userInput;
          }
    //line number 80 will add the values of the userInput together.     
    count2+=userInput;

// line 83 is a counter that holds the number of times the loop
// as excuted 
    count3++;
      // line 88 will get a grade point average by dividing count3
// by count2
   cout << fixed << showpoint << setprecision(2);
   gpa = count2/count3;


      } while(userInput !='X' && userInput!='x');


     cout << "Total Grade Point: " << count2 << endl;
     cout << "GPA: " << gpa << endl;
    }

如果我的问题太模糊，请告诉我，以便我澄清。

Answer 1

如果您查看 ASCII 表，您会发现字母只是数字。

http://www.asciitable.com/

您可以使用简单的减法计算偏移量：

'a' - 'a' == 0
'b' - 'a' == 1
'c' - 'a' == 2

等等。要将其转换为 GPA 成绩，您可以进行简单的转换：

int deltaA = (int)('a' - 'a'); // explicit cast to int is not really needed
int max = 4;
int grade = max - deltaA;

另一种解决方案是使用地图：

std::map<char, int> grades;
grades['a'] = 4;
grades['b'] = 3;
grades['c'] = 2;
...
int score = grades['a']; // score == 4

最好使用大写或小写字母。您可以使用int std::tolower(int ch) 和int std::toupper(int ch) 函数转换它们。将 char 放入 int 是可以的 - 两者都是整数，int 的范围更广，char 适合。

反过来 - 没那么容易。 int 的范围比 char 更宽，您应该在转换回来之前检查您的 int 值是否在 char 范围内。

Answer 2

有几件事...

字符 A, a = 4; 创建字符 VARIABLES（存储位置）并为变量 a 赋值 4。变量代表一个内存位置，一个存储信息的地方。它是此存储位置的人类可读表示。它不是一种翻译机制。 CHARACTER 'a' 是一个用 ascii 码表示的值，可以存储在变量中，十六进制值为 61 或十进制 97。变量 a 与字符值 'a' 不同。并将十进制 4 存储到字符变量中是将其设置为 EOT 字符。

最好的办法是使用开关。它工作正常。

最好在使用变量之前对其进行初始化。您的计数器可能会从零开始，但取决于编译器，它们可能包含随机值。在进入循环之前将它们设置为零。

Answer 3

感谢大家的帮助。这就是我解决问题的方法。前段时间想发的，忘记发了。

char userInput;

// the for loop is to make sure program will only run 3 times
for (int i=1; i<4;i++)
{
 int count2 = 0;
 double count3 = 0.0;
 double gpa;
 cout << "Test #" << i << ":" << endl;
 cout << endl;

  // the do while loop is being used to ensure that the user gets to
  // input at least once.
  do
  {
    cout << "Enter a Letter Grade (enter 'X' to exit): ";
    cin >> userInput;

      // the while loop is only being used for input validation.
      while (userInput!='A' && userInput!='a' && userInput!='B' &&
             userInput!='b' && userInput!='C' && userInput!='c' &&
             userInput!='D' && userInput!='d' && userInput!='F' &&
     userInput!='f' && userInput !='X' && userInput !='x')
  {
cout << "\n Invalid letter grade, please try again.\n";
cout << "\n Enter Letter Grade (enter 'X' to exit):";
cin >> userInput;
  }

  if(userInput !='X' && userInput !='x')
  {
int grade=func(userInput);

// count2 will add the values of the userInput together
count2+=grade;

// count3 is a counter that holds the number of times the loop
// as execute.
count3++;
  }
cout << fixed << showpoint << setprecision(2);
// to get the grade point avarage you need to divide count3 by count2
  gpa = count3/count2;

 } while(userInput !='X' && userInput!='x');

 // the next few lines will display the information gathered
 cout << endl;
 cout << "Total Grade Points: " << count2 << endl;
 cout << "GPA: " << gpa << endl;
 cout << endl;
 cout << endl;

}

 return 0;
}


int func(char userInput)
 {
// grade is being set to zero so there is a less chance of getting wrong
// data        
int grade=0;
// this will make the userInput into a capital letter
userInput=toupper(userInput);
// we are setting value to equal the ascii number of the chosen
// letter
int value=userInput; // if input='A' then value = 65
// by subtracting 69 by the value it will help get us the point value
// we need.
grade=69-value;   // gpa=4
// if the number value of grade becomes negative it will assign grade
// to store the number 0
if(grade<0)grade=0;
return grade;
}