如何解决C ++添加数组
我是C ++的新手，目前已参加入门课程。我正在创建的程序是编程教程（具有讽刺意味的！），当前正在尝试添加菜单选项，该菜单选项会将用户带到测验中。没有什么花哨。截至目前，似乎我的函数无法识别我创建的类。到目前为止，这就是我的建议，我们将不胜感激任何精打细算的建议！
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
int main()
{
string username = "";
int choice;
char c;
char answer;
int x = 4;
int y = 5;
int z = x + y;
int ans;
int total;
class Question
{
private:
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
public:
void setValues(string,string,int,int);
void askQuestion ( );
};
//welcome message
cout << "Hello user,please enter your name:";
cin >> username;
cout << "Welcome to the programming tutorial " << username << "."<< endl;
//menu selection
while(toupper (choice != 'E'))
{
cout << "What would you like to do? (Unit 1 - Declaring Variables (1),Unit 2 - Input/ Output (2),Unit 3 - Conditionals (3),Quizzes (4) or Exit (E))";
cin >> choice;
if (choice == '1')
{
cout << "We will begin with defining variables. The first step to doing this is choosing which datatype your variable is.\n";
cout << "The following are a few of the common datatypes used in programming.\n";
cout << "Character ==> char\n";
cout << "Integer ==> int,long,double\n";
cout << "Boolean ==> bool\n";
cout << endl;
cout << "When declaring a variable,you must put its datatype before the variable name.\n";
cout << "An example of this would be if we wanted to declare the value of x as 4.\n";
cout << "We would write this as: \n";
cout << "int x = 4\n";
cout << "The program will now use the value 4 for the variable name 'x'\n";
cout << endl;
cout << "Now let's assume we assigned the value of 5 to the variable 'y'\n";
cout << "If we wanted to add x and y and assign the sum to the variable 'z',we would write:\n";
cout << "int z = x + y\n";
cout << "Now when we use the variable 'z' in our program,it will perform the calculation given x=4 and y=5 and declare 9 as the value of the variable 'z'.\n";
cout << "To test our code,we would write: " << endl;
cout << "cout<<'x + y'<< z << endl; \n";
cout << "If written correctly,it will display as: \n";
cout << "x + y = " << z << "." << endl;
}
if (choice == '2')
{
cout << "Now that we understand the basics of declaring variables,let's discuss displaying,or output of,information to a user.\n";
cout << "If you wanted to display a welcome message,for example,you would type:\n";
cout << "cout << 'Welcome';\n";
cout << "The line of code would start with 'cout' followed by two less than signs and then the message you wish to display in quotes.\n";
cout << "Using this,you can ask the user for input.\n";
cout << "Enter c to continue...";
cin >> c;
cout << "Let's say we have a program that flips a coin. You may want to ask the user how many times to flip the coin.\n";
cout << "Assuming we previously declared this amount variable as 'int timesFlipped',we would 'cout' our question and the next line would read:\n";
cout << "cin>> timesFlipped; \n";
cout << "This will store the users input for the variable 'timesFlipped'\n";
cout << "You almost always end a line of code with a semi colon."<<endl;
}
if (choice == '3')
{
cout << "This unit will cover conditional expressions."<<endl;
}
if (choice == '4')
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
Question q1;
Question q2;
Question q3;
cout <<username << ",you have chosen to take a quiz." << endl << endl;
int ans,score = 0;
cout << "Unit One Quiz - Variables " << endl << endl;
q1.setValues("How would you declare the value of 'x' as 12? ","x=12()","x==12()","x=12;()",3,1);
q2.setValues("What do you need to put before a variable when declaring it?","a name()","a value()","a datatype()",1);
q3.setValues("Which data type would you use for a number that includes a decimal value?","int()","double()","float()",2,1);
q1.askQuestion();
q2.askQuestion();
q3.askQuestion();
cout << "Your score out of a possible 3 is " << total << endl;
}
if (choice == 'E')
{
cout << "Have a good day!";
break;
}
}
system("pause");
}
void Question :: setValues(string q,string a1,string a2,string a3,int ca,int pa)
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
Question_Text = q;
Answer_one = a1;
Answer_two = a2;
Answer_three = a3;
Correct_Answer = ca;
Question_Score = pa;
}
void Question :: askQuestion()
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
int ans;
int Total;
cout << endl;
cout << Question_Text << endl;
cout << "1. " << Answer_one << endl;
cout << "2. " << Answer_two << endl;
cout << "3. " << Answer_three << endl << endl;
cout << "Please enter your answer: " << endl;
cin >> ans;
if (ans == Correct_Answer)
{
cout << "That is correct!" << endl;
Total = Total + Question_Score;
}
else
{
cout << "Sorry,that is incorrect" << endl;
cout << "The correct answer was " << Correct_Answer << endl;
}
}
我在这两个函数中都声明了变量，因为直到我这样做时才在每个函数中都识别出它们，但是现在我在想这是因为无法识别该类。 >
解决方法
针对您遇到的问题，您的程序可以简化为以下内容：
int main()
{
class Question {
public:
void askQuestion();
};
Question q;
q.askQuestion();
}
void Question::askQuestion() { }
在Question::askQuestion()的定义中会出现错误，因为该类是在main()函数的范围内声明（并定义）的-在它的外部无法识别。
将班级移到main()之外，就像这样：
class Question {
public:
void askQuestion();
};
int main()
{
// you can use the Question class here,even though you haven't
// defined all of its methods yet!
Question q;
q.askQuestion();
}
void Question::askQuestion() { }
...，并且此程序执行compile（godbolt.org）。
这还不是全部，但是...您要在每个成员函数中声明成员变量（例如Question_text）。本地定义掩盖了类成员，因此您只需设置方法的本地变量，该变量在执行完成时会被破坏。
其他注意事项和建议：
- 如果类已经有了方法名称，则无需在方法名称中再次使用单词
Question。即Question::ask()比Question::askQuestion()似乎是更好的名称选择。Question::Question_text也是如此。 - 最好使用avoid using namespace std，并且仅使用您专门打算引用的
std::中的类，类型或函数。 - 如果考虑一下，对
Question类的使用是相当人为的。它的代码主要是用于进行测验的代码，而不是诸如此类的问题。似乎最好选择“对象”是一组答案和值或问题参数。可以通过构造QuestionParameters对象来设置值，并提出问题可能是采用此类对象的函数。 - 如果您有
Answer_one，Answer_two，Answer_three-那么您可能需要一个容器，例如std::vector<std::string> answers。然后，您可以使用答案索引而不是使用if或switch语句。
在主函数之外定义类时必须进行的更改 使用开关代替if 使用int值而不是E退出程序。 我对代码进行了如下更改
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
class Question
{
private:
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
public:
void setValues(string,string,int,int);
void askQuestion();
}; //end of class
//---------------------------
void Question ::askQuestion()
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
int ans;
int Total;
cout << endl;
cout << Question_Text << endl;
cout << "1. " << Answer_one << endl;
cout << "2. " << Answer_two << endl;
cout << "3. " << Answer_three << endl
<< endl;
cout << "Please enter your answer: " << endl;
cin >> ans;
if (ans == Correct_Answer)
{
cout << "That is correct!" << endl;
Total = Total + Question_Score;
}
else
{
cout << "Sorry,that is incorrect" << endl;
cout << "The correct answer was " << Correct_Answer << endl;
}
} //end of askQuestion
//----------------------------------
void Question ::setValues(string q,string a1,string a2,string a3,int ca,int pa)
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
Question_Text = q;
Answer_one = a1;
Answer_two = a2;
Answer_three = a3;
Correct_Answer = ca;
Question_Score = pa;
} //end of setValues
//----------------------------------
int main()
{
string username = "";
int choice;
char c;
char answer;
int x = 4;
int y = 5;
int z = x + y;
int ans;
int total;
//welcome message
cout << "Hello user,please enter your name:";
cin >> username;
cout << "Welcome to the programming tutorial " << username << "." << endl;
//menu selection
while (choice != 5)
{
cout << "What would you like to do? (Unit 1 - Declaring Variables (1),Unit 2 - Input/ Output (2),Unit 3 - Conditionals (3),Quizzes (4) or Exit (5))";
cin >> choice;
switch (choice)
{
case 1:
{
cout << "We will begin with defining variables. The first step to doing this is choosing which datatype your variable is.\n";
cout << "The following are a few of the common datatypes used in programming.\n";
cout << "Character ==> char\n";
cout << "Integer ==> int,long,double\n";
cout << "Boolean ==> bool\n";
cout << endl;
cout << "When declaring a variable,you must put its datatype before the variable name.\n";
cout << "An example of this would be if we wanted to declare the value of x as 4.\n";
cout << "We would write this as: \n";
cout << "int x = 4\n";
cout << "The program will now use the value 4 for the variable name 'x'\n";
cout << endl;
cout << "Now let's assume we assigned the value of 5 to the variable 'y'\n";
cout << "If we wanted to add x and y and assign the sum to the variable 'z',we would write:\n";
cout << "int z = x + y\n";
cout << "Now when we use the variable 'z' in our program,it will perform the calculation given x=4 and y=5 and declare 9 as the value of the variable 'z'.\n";
cout << "To test our code,we would write: " << endl;
cout << "cout<<'x + y'<< z << endl; \n";
cout << "If written correctly,it will display as: \n";
cout << "x + y = " << z << "." << endl;
break;
}
case 2:
{
cout << "Now that we understand the basics of declaring variables,let's discuss displaying,or output of,information to a user.\n";
cout << "If you wanted to display a welcome message,for example,you would type:\n";
cout << "cout << 'Welcome';\n";
cout << "The line of code would start with 'cout' followed by two less than signs and then the message you wish to display in quotes.\n";
cout << "Using this,you can ask the user for input.\n";
cout << "Enter c to continue...";
cin >> c;
cout << "Let's say we have a program that flips a coin. You may want to ask the user how many times to flip the coin.\n";
cout << "Assuming we previously declared this amount variable as 'int timesFlipped',we would 'cout' our question and the next line would read:\n";
cout << "cin>> timesFlipped; \n";
cout << "This will store the users input for the variable 'timesFlipped'\n";
cout << "You almost always end a line of code with a semi colon." << endl;
break;
}
case 3:
cout << "This unit will cover conditional expressions." << endl;
break;
case 4:
{
string Question_Text;
string Answer_one;
string Answer_two;
string Answer_three;
int Correct_Answer;
int Question_Score;
Question q1;
Question q2;
Question q3;
cout << username << ",you have chosen to take a quiz." << endl
<< endl;
int ans,score = 0;
cout << "Unit One Quiz - Variables " << endl
<< endl;
q1.setValues("How would you declare the value of 'x' as 12? ","x=12()","x==12()","x=12;()",3,1);
q2.setValues("What do you need to put before a variable when declaring it?","a name()","a value()","a datatype()",1);
q3.setValues("Which data type would you use for a number that includes a decimal value?","int()","double()","float()",2,1);
q1.askQuestion();
q2.askQuestion();
q3.askQuestion();
cout << "Your score out of a possible 3 is " << total << endl;
break;
}
case 5:
cout << "Have a good day!";
break;
} //end of switch
} //end of while
system("pause");
return 0;
} //end of main
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