Take input from a file and check The number is prime or not

Question

In c++ I try to take input from a file and check if the number is prime or not. But the main problem is if one of the number isn't prime then next numbner is showng not prime ex-

my input in a file is 1 2 3 4 5 6

for first 3 digit it shows prime number when print num4 it says not prime after that all the input says not prime. Wht's the problem here is my code-

int main()
{
int x,i,b=0,j;


int  a[15];//size of array more than number of entries in data file
ifstream infile;

infile.open("prog1_input.txt");//open the text file

if (!infile)
{
    cout << "Unable to open file";
    exit(1); // terminate with error
}

i=0;

while (!infile.eof())
{
    //To make array for column
    infile>>x;


    a[i]=x;


    for(j=2;j<x;j++)
    {
        if(x%j==0)
        {
            b++;
        }
    }


    if(b==0)
    {
        cout<<a[i]<<"\t"<<"Prime"<<endl;

    }

    else

       cout<<a[i]<<"\t"<<"Not Prime"<<endl;



    // cout <<a[i]<<endl;
    i++;

}
// To print entry
infile.close();
// getch();

}

Answer 1

in your code, b is never reset back to 0

What you need to do is this

if(b==0)
{
    cout<<a[i]<<"\t"<<"Prime"<<endl;

} else {

   cout<<a[i]<<"\t"<<"Not Prime"<<endl;
   b = 0;
}

Answer 2

At first glance i would say that you have to reinitialize b at the beginning of the loop

 if (!inline.eof())

If you have any question, please you are welcome :)