#include <iostream.h>
#include <string.h>
void main()
{char a[102];
int b[100],i,n;
for (i=0;i<n;i++)
cin>>a;
for(i=0;i<n;i++)
{ b[i]= int(a[i]- 'a');
if(i==0){if(b[i]<5)
b[i]+=26;
cout<<char(b[i]-5+'a');}}
else  {if(b[i]<b[i-1]) b[i]+=26;
coun<<char(b[i]-b[i-1]+'a');}}
i don't understed where is my mistake

Why you use n?