C++ 检查整数。
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C++ Checking for an integer.
提问by xavi
New to C++. Having issues correctly looping while handling errors. I am trying to check if user input is an integer, and is positive.
C++ 新手。在处理错误时正确循环出现问题。我试图检查用户输入是否是整数，并且是正数。
do{
cout << "Please enter an integer.";
cin >> n;
if (cin.good())
{
if (n < 0) {cout << "Negative.";}
else {cout << "Positive.";}
}
else
{
cout << "Not an integer.";
cin.clear();
cin.ignore();
}
}while (!cin.good() || n < 0);
cout << "\ndone.";
When a non-integer is entered, the loop breaks. I feel like I am misunderstanding the inherent usage of cin.clear()and cin.ignore()and the status of cinduring this loop. If I remove the cin.ignore(), the loop becomes infinite. Why is this? What can I do to make this into an elegantly functioning loop? Thank you.
当输入非整数时，循环中断。我觉得我在这个循环中误解了cin.clear()andcin.ignore()和 status的固有用法cin。如果我删除cin.ignore()，循环将变得无限。为什么是这样？我该怎么做才能使它成为一个优雅运行的循环？谢谢你。
采纳答案by Paul R
In your non-integer branch you are invoking further cinmethods so cin.good()gets reset to true.
在您的非整数分支中，您正在调用更多cin方法，因此cin.good()被重置为 true。
You could change your code to something like this:
您可以将代码更改为如下所示：
while(1) { // <<< loop "forever"
cout << "Please enter an integer.";
cin >> n;
if (cin.good())
{
if (n < 0) {cout << "Negative.";}
else { cout << "Positive."; break; }
} // ^^^^^ break out of loop only if valid +ve integer
else
{
cout << "Not an integer.";
cin.clear();
cin.ignore(INT_MAX, '\n'); // NB: preferred method for flushing cin
}
}
cout << "\ndone.";
or you can simplify it even further like this:
或者您可以像这样进一步简化它：
while (!(cin >> n) || n < 0) // <<< note use of "short circuit" logical operation here
{
cout << "Bad input - try again: ";
cin.clear();
cin.ignore(INT_MAX, '\n'); // NB: preferred method for flushing cin
}
cout << "\ndone.";
回答by imulsion
int n;
while (!(cin >> n)||n<0)//as long as the number entered is not an int or negative, keep checking
{
cout << "Wrong input. Please, try again: ";
cin.clear();//clear input buffer
}
//only gets executed when you've broken out of the while loop, so n must be an int
cout << "Positive.";
cout << "\ndone.";//finished!
Should do what you want.
应该做你想做的。
