C++ 如何避免 int 变量的字符输入？
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How Can I avoid char input for an int variable?
提问by Scoop
The program below shows a 'int' value being entered and being output at the same time. However, when I entered a character, it goes into an infinite loop displaying the previous 'int' value entered. How can I avoid a character being entered?
下面的程序显示了同时输入和输出的“int”值。但是，当我输入一个字符时，它会进入一个无限循环，显示之前输入的“int”值。如何避免输入字符？
#include<iostream>
using namespace std;
int main(){
int n;
while(n!=0){
cin>>n;
cout<<n<<endl;
}
return 0;
}
回答by Anirudh Ramanathan
Reason for Infinite loop:
无限循环的原因：
cin goes into a failed state and that makes it ignore further calls to it, till the error flag and buffer are reset.
cin 进入失败状态，这使得它忽略对它的进一步调用，直到错误标志和缓冲区被重置。
cin.clear();
cin.ignore(100, '\n'); //100 --> asks cin to discard 100 characters from the input stream.
Check if input is numeric:
检查输入是否为数字：
In your code, even a non-int type gets cast to int anyway. There is no way to check if input is numeric, without taking input into a char array, and calling the isdigit()function on each digit.
在您的代码中，即使是非 int 类型也会被强制转换为 int。没有办法检查输入是否为数字，而不将输入输入到字符数组中，并isdigit()在每个数字上调用函数。
The function isdigit()can be used to tell digits and alphabets apart. This function is present in the <cctype>header.
函数isdigit()可用于区分数字和字母。此函数存在于<cctype>标题中。
An is_int() function would look like this.
is_int() 函数看起来像这样。
for(int i=0; char[i]!='#include <iostream>
#include <climits> // for INT_MAX limits
using namespace std;
int main()
{
int num;
cout << "Enter a number.\n";
cin >> num;
// input validation
while (cin.fail())
{
cin.clear(); // clear input buffer to restore cin to a usable state
cin.ignore(INT_MAX, '\n'); // ignore last input
cout << "You can only enter numbers.\n";
cout << "Enter a number.\n";
cin >> num;
}
}
';i++){
if(!isdigit(str[i]))
return false;
}
return true;
回答by user1480872
If you want use user define function you can use the ascii/ansi value to restrict the char input.
如果您想使用用户定义函数，您可以使用 ascii/ansi 值来限制字符输入。
48 -57 is the range of the 0 to 9 values
48 -57 是 0 到 9 值的范围
