C program to find a given number is prime or not using a flag variable

Following program reads a number from the user and prints whether it is prime or not by using a flag variable. A flag variable is a binary variable with values 0 and 1:

/*Program to find the given number is prime number or not using a flag variable*/
main()
{
    int number,i,flag=0;
    clrscr();
    printf("Enter the number:");
    scanf("%d",&number);
    for(i=2;i<=number-1;i++)
    {
        if(number%i==0)
        {
            flag = 1;
        }
    }
    if(flag==1)
    {
        printf("\n%d is not a prime number",number);
    }
    else if(number<=1)
    {
        printf("\n%d is invalid number!",number);
    }
    else
    {
        printf("\n%d is a prime number",number);
    }
    getch();
}
Sample input and output:
Enter the number:17

17 is a prime number