Determine whether to digital in c++

Ken H

14y2.1k

hi all,

#include
using namespace std;
int main()
{
bool isDigit(int isd);
int unknowNUM;
cout<<"please input one integer number:"< cin>>unknowNUM;
if(isDigit(unknowNUM))
{
//Things to do...

}
else
   {
     cout<<"you just input not digit!"<   }

return 0;
}
bool isDigit(int isd)
{
   if (/*if "isd" is digit */) return true;
   else if(/*if "isd" no digit*/)return false;
}

thanks

6 Replies

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Vulpes14y ago
Accepted answer
If you're wanting to check that several characters entered at the console represent an integer, then I wouldn't use isDigit - I'd declare unknownNUM to be an int and then use cin.fail() to check whether it is or not.

If it isn't then you can clear the stream and the buffer and continue looping until a valid integer is entered:

#include
using namespace std;

int main()
{
int unknowNUM;

while(true)
{
cout<<"please input one integer number:"<
cin>>unknowNUM;
if(!cin.fail()) break; // it's an integer so break from while loop
cout<< "Not a valid integer, try again"<
cin.clear();
cin.ignore(numeric_limits::max(),'\n');
}

if(unknowNUM > 100)
{
cout<<"An integer greater than 100"<
}
else if(unknowNUM < 150)
{
cout<<"An integer less than 101 (in effect)"<
}

return 0;
}
Ken H14y ago
thank for Vulpes .
Ken H14y ago
The question now is,I need to "unknowNUM" a logical comparison operator
such as:<,>,<=,>=,!=,==
assume unknowNUM the value is 100
if(isDigit(unknowNUM))
{
     if(unknowNUM>100)
     {
      //do...
     }
     else if(unknowNUM<150)
     {
      //do...
     }
}

thanks
Ken H14y ago
To determine the user input is numeric.
thank for Mahesh Chand,Vulpes.
Vulpes14y ago
It sounds to me that you want to test whether a character entered at the console is a digit (0 to 9) or not.

If so, then you can't use 'int' as the type of unknownNUM because this pre-supposes that unknownNUM is an integer in the first place.

I'd suggest that you use unsigned char instead:

#include
using namespace std;

int main()
{
bool isDigit(unsigned char isd);
unsigned char unknowNUM;
cout<<"please input one integer number:"<
cin>>unknowNUM;

if(isDigit(unknowNUM))
{
//Things to do...
}
else
{
cout<<"you haven't input a digit!"<
}

return 0;
}

bool isDigit(unsigned char isd)
{
if (isd >= '0' && isd <= '9') return true;
return false;
}
Mahesh Chand14y ago
And what is your question?