please give some test

#include <stdio.h>
int main()
{
    int string[200];
    int len=0;
    char ch;
    int count;
    ch=getchar();
    while(!((ch=='\0')||(ch=='EOF')||(ch=='\n')))
    {
        string[len]=ch-'a';
        len++;
        ch=getchar();
    }
    string[len]='\0';
    //perviy prohod
    if(len==1)
    {
        printf("%c\0",string[0]-5);
        return 0;
    }
    if (string[0]<5)
        string[0]+=26;
    for(count=1;count<len;count++)
    {
        while(string[count]<string[count-1])
            string[count]=string[count]+26;
    }
    //vtoroy prohod
    for(count=len-1;count>0;count--)
    {
        string[count]=string[count]-string[count-1];
    }
    string[0]=string[0]-5;
    //tretiy prohod
    for(count=0;count<len;count++)
    {
        printf("%c",string[count]+'a');
    }
    printf("\0");
    return 0;
}

i find my mistake. don't forget about case,when you have 1 symbol!
/////////////WA 14//////////
if(len==1)
{
printf("%c\0",string[0]-5);
return 0;
}
///////////////AC////////////
if(len==1)
{
if (string[0]<5)
string[0]+=26;
printf("%c\0",string[0]-5+'a');
return 0;
}