是/否程序在 C++ 中使用 while 循环
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Yes/No program using while loop in C++
提问by Horsey Potato
I'm trying to make a program that asks the user whether they would like to continue to the next calculation. For some reasons whenever I enter y or Y, the program ends. However, if I use only one condition inside the if statement(without '||'sign), the code works fine. I just want to make sure that the user can enter both upper and lower case.
我正在尝试制作一个程序，询问用户是否愿意继续进行下一次计算。由于某些原因，每当我输入 y 或 Y 时，程序就会结束。但是，如果我在 if 语句中只使用一个条件（没有 '||' 符号），则代码工作正常。我只想确保用户可以输入大写和小写。
What's wrong with the code? Is there a better way to do this?
代码有什么问题？有一个更好的方法吗？
int main()
{
char choice;
while(true)
{
cout<<"Would you like to perform other calculation?(Y/N)"<<endl;
cin >> choice;
if(choice == 'Y'|| choice =='y'){
return true;
}else if(choice =='N'||choice =='n'){
return false;
}
}
return 0;
}
回答by Treycos
The returnstatement ends a function, in this case, this is the main, so it ends your program, whatever value you're returning.
If you only want to get out of your loop you have two solutions:
Use a boolean:
该return语句结束的功能，在这种情况下，这是主要的，因此结束你的程序，你就返回任何值。
如果您只想退出循环，您有两种解决方案：
使用布尔值：
int main()
{
char choice;
bool run = true; //@stefaanv
while(run)
{
// Make your calculation
cout<<"Would you like to perform other calculation?(Y/N)"<<endl;
cin >> choice;
if(choice =='N'||choice =='n'){
run = false;
}
}
return 0;
}
Use breakto exit your loop:
使用break退出你的循环：
int main()
{
char choice;
while(true)
{
// Make your calculation
cout<<"Would you like to perform other calculation?(Y/N)"<<endl;
cin >> choice;
if(choice =='N'||choice =='n'){
break;
}
}
return 0;
}
But both these solution will consider any character entered exept N/n as "continue", if you want to avoid this:
但是，如果您想避免这种情况，这两种解决方案都会将除 N/n 之外输入的任何字符视为“继续”：
int main()
{
char choice;
bool run = true;
while(run)
{
// Make your calculation
do{
cout<<"Would you like to perform other calculation?(Y/N)"<<endl;
cin >> choice;
choice = tolower(choice);//Put your letter to its lower case
}while (choice != 'n' && choice != 'y')
if(choice =='n'){
run = false;
}
}
return 0;
}
回答by Christian Dean
For some reasons whenever I enter y or Y, the program ends
由于某些原因，每当我输入 y 或 Y 时，程序就会结束
The returnstatement is used to return control(and sometimes an optional value), to a functions caller. When return is used inside the called function, the function is terminated. From cppreference.com:
该return语句用于将控制（有时是可选值）返回给函数调用者。当在被调用函数内使用 return 时，函数将终止。来自 cppreference.com：
[return] terminates [the] current function and returns [a] specified value to the caller function.
[return]终止 [the] 当前函数并将 [a] 指定值返回给调用者函数。
(emphasis mine)
（强调我的）
You may be under the impression that the statement return trueinside your while-loop is returning the Boolean value of true to your while condition. It is not.
您可能认为return truewhile 循环中的语句将布尔值 true 返回到您的 while 条件。它不是。
If your end goal is to create a yes/no style program that ends when the user enters "No/no", then you can to make use of the continueand breakstatements, or use a do/whileloop.
如果您的最终目标是创建一个是/否风格的程序，当用户输入“否/否”时结束，那么您可以使用continueandbreak语句，或使用do/while循环。
Using continueand break
使用continue和break
The continuestatement is used to immediately skip to the next iteration of a loop, for or while, terminating the current iteration. From cppreference.com:
该continue语句用于立即跳到循环的下一次迭代，for 或 while，终止当前迭代。来自 cppreference.com：
Causes the remaining portion of the enclosing for, range-for, while or do-while loop body to be skipped. Used when it is otherwise awkward to ignore the remaining portion of the loop using conditional statements.
使封闭的 for、range-for、while 或 do-while 循环体的剩余部分被跳过。当使用条件语句忽略循环的剩余部分很尴尬时使用。
(emphasis mine)
（强调我的）
The breakstatement is somewhat similar to continue, but instead of breaking the current iteration and skipping to the next one, it immediately breaks the entire program out of the while loop returning control to the outer-scope. From cppreference.com:
该break语句有点类似于continue，但它不是中断当前迭代并跳到下一个迭代，而是立即将整个程序从 while 循环中中断，将控制权返回到外部作用域。来自 cppreference.com：
Causes the enclosing for, range-for, while or do-while loop or switch statement to terminate.Used when it is otherwise awkward to terminate the loop using the condition expression and conditional statements.
导致封闭的 for、range-for、while 或 do-while 循环或 switch 语句终止。当使用条件表达式和条件语句终止循环很尴尬时使用。
(emphasis mine)
（强调我的）
After examining the information above, you can modify your program to make use of continueand break, instead of return:
检查上述信息后，您可以修改您的程序以使用continueand break，而不是return：
#include <iostream>
using namespace std; // This is for demonstration purposes ONLY
// never use this statement in your actual program. prefix cout and
// cin with std::
int main()
{
char choice;
while(true)
{
cout<<"Would you like to perform other calculations?(Y/N)"<<endl;
cin >> choice;
if(choice == 'Y'|| choice =='y'){
continue; // instead of returning, skip to the next iteration
// and ask again
}else if(choice =='N'||choice =='n'){
break; // return could be used here to break the while loop and
// terminate the program. But be explicit and use a statement specifically
// made for breaking out of loops
}
}
return 0;
}
Using a do/whileloop
使用do/while循环
While the method above would work, I recommend using my second option-- a do/whileloop. The do/whilehas the advantage o being shorter, and not having to make use of any kind of major control flow. From cppreference:
虽然上述方法可行，但我建议使用我的第二个选项——do/while循环。在do/while具有优势o为短，不必使用任何一种主要的控制流的。来自 cppreference：
Executes a statement repeatedly, until the value of expression becomes false. The test takes place after each iteration.
重复执行一条语句，直到表达式的值变为假。测试在每次迭代后进行。
If needed you could even add error checking to validate a users input:
如果需要，您甚至可以添加错误检查来验证用户输入：
#include <iostream>
using namespace std; // This is for demonstration purposes ONLY
// never use this statement in your actual program. prefix cout and
// cin with std::
int main()
{
char choice;
do { // do everything in the do block while...
cout <<"Would you like to perform other calculations?(Y/N)"<< endl;
cin >> choice;
if (choice != 'Y' and choice != 'y' and choice != 'N' and choice != 'n') // if needed add input
cout << choice << " is not a valid option. Try agian" << endl; // validation
} while (choice !='N' && choice !='n'); // the user input does not equal 'N'andr 'n'
return 0;
}
Output
输出
Would you like to perform other calculations?(Y/N)
y
Would you like to perform other calculations?(Y/N)
Y
Would you like to perform other calculations?(Y/N)
n
References and Resources
参考资料和资源
回答by Horsey Potato
I just wrote some code and it works like a charm using "goto". The code also included data validation as well. Many thanks to @Treycos.
我刚刚写了一些代码，它使用“goto”就像一个魅力。该代码还包括数据验证。非常感谢@Treycos。
int main()
{
char choice ='Y';
bool valid = true;
//some calculation
here:
int x =1+1;
cout<<x<<endl;
while(valid){
cout<<"Would you like to perform other calculation?(Y/N)"<<endl;
cin >> choice;
if(choice =='N' || choice =='n'){
break;
}
if(choice =='Y'||choice =='y'){
goto here;
}
else if(choice != 'N'&& choice != 'n'&&choice != 'Y'&&choice != 'y'){
cout<<"Invalid input."<<endl;
valid = true;
}
}
return 0;
}
Output:
输出：
2
Would you like to perform other calculation?(Y/N)
y
2
Would you like to perform other calculation?(Y/N)
Y
2
Would you like to perform other calculation?(Y/N)
$
Invalid input.
Would you like to perform other calculation?(Y/N)
n
Process returned 0 (0x0)
For uppercase n:
对于大写 n：
2
Would you like to perform other calculation?(Y/N)
N
Process returned 0 (0x0)
