array length and array stop in C

I have an array that contains letters. The length of the array is 100 If the user enters more than 100 characters, he should receive an error message If it is less than 100 characters then the program will work

int main()
{
    char line[100];
    int vowels, consonants, i;
    vowels = consonants = i = 0;

    printf("\n Please Enter any lineing :  ");
    scanf("%s", line);

    while (line[i] != 0 )
    {
        if ( **What should I write here !!** )
        {
            printf("error"); 
        }
        return 0;
}