Code is working but the Gradebook checks are failed

Question

My program is working correctly but all checks on the Gradebook have failed.

I think problem is in printf, but what is the reason?

I just print a few words and after that at new line the program will get a string.

int main (int arg , string arv [])
{

    if (arg != 2)
    {
        printf ("Usage: ./ceasar.c key \n");
        return 1;
    }

    int k = atoi(arv[1]);
    int low_let = 'a';
    int up_let = 'A';

    printf("Enter string: \n");
    string s = GetString();
    string encr = s;

    for (int i = 0; i < strlen(s); i++)
    {
        if ( isalpha(s[i]))
        {

Some clarification: I have a different problem than in I can't get any grade on Gradebook because some programs were successfully checked:

and my test results look good:

jharvard@appliance (~/Dropbox/pset2): ./caesar 1
Enter string: 
a
b 
jharvard@appliance (~/Dropbox/pset2): ./vigenere BaZ
Enter string: 
BaRFoo
CaQGon   

Problem with check50 was solved after running command update50 more details can be found here: Why does check50 fail with status code 400?

Answer 1

a bit the same problem was here and in my case it wasn't been obvious: Script which is using for checking, is expecting to get a result at the second OUTPUT row. And my code will return only blank row, a bit strange bug.

printf("Enter string: \n");      -- 1 row

string s = GetString();          -- 2 row         BaRFoo

                                 -- 3 row answer  CaQGon

I saw it another question, but there problem was a bit different.

for check50 error 400 necessary to run command from terminal: update50

More details youcan find here: Why does check50 fail with status code 400?