C :

#include <stdio.h>
#include <string.h>

int main()

{
    char s[1001];
    int i;
    while(gets(s))
    {
        for(i = 0;i < strlen(s);i++)
        {
            if(s[i] >= 'a' && s[i] < 'z')
                s[i] += 1;
            else if(s[i] == 'z')
                s[i] -= 25;
        }
        puts(s);
    }
    return 0;
}

C++ :

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
	string s;
	getline(cin,s);
	for(int i=0;i<=s.size()-1;++i)
	{
		if(s[i]==' ')
		  continue;
		if(s[i]>='1'&&s[i]<='9')
		  continue;
		if(s[i]>='a'&&s[i]<='z')
		{
		  if(s[i]=='z')
		  {
			s[i]-=25;
			continue;
		  }    
		  if(s[i]!='z')
		  {
		  	s[i]++;
		  	continue;
		  }
		}
	}
	for(int i=0;i<=s.size()-1;++i)
	  cout<<s[i];
}

Python :

# coding=utf-8
letters='abcdefghijklmnopqrstuvwxyza'
S=input()
for i in S:
    if i in letters:
        index=(letters.find(i)+1)
        print(letters[index],end='')
    else:
        print(i,end='')