检查输入是否为整数或大于零

Question

so im struggling a bit - how can i make function to check if the user input is integer? I did try do/while... but somehow its not working.

void pievieno(int *a ,int jaunais,int vecais){
int jaunais_skaitlis;
cout<< "Ievadiet skaitlus" <<endl;
for (int i=vecais;i<jaunais;i++) 

{
    cin >> jaunais_skaitlis;
    a[i] = jaunais_skaitlis;
}

Thanks in advance!

Answer 1

Well, there's no point in checking the data type of user's input because you've deliberately defined the input variable to be an integer using int jaunais_skaitlis; . Therefore, no matter what the user types in, you're getting and integer value for the input anyways.

However, what you can do it define the data type to be something other than integer , maybe a float , and then check if its an integer, float or something else.

Answer 2

You should accept user's input with string, and check what's in it. There's lots of method to check user's input. The most powerful way is regex.

Answer 3

When you call stream >> variable , depending of type of variable , the stream will try to process characters in order to get something, which is a valid for such variable type. If it fails to do so, stream s failbit is set, so you can check that.

for (int i=vecais;i<jaunais;i++) 
{
    cin >> jaunais_skaitlis;
    if (cin.fail())
    {
        // abort, user inputed something, which is not integer.
    }
    a[i] = jaunais_skaitlis;
}

Beware, that stream will do as much as it can to actually extract something from the input. Thus, if you enter 123qffe541e , it actually is valid input, jaunais_skaitlis will contain 123 and rest of characters will remain in the stream (thus, failing next iteration).

If you really want to check if whole input is integer, you have to read more chars (eg read to std::string , either single word or whole line, depending on your needs) and then process that.