C :

#include <stdio.h>

int main()
{
	int c;
	while ((c = getchar()) != EOF) 
	{
		if (c >= 'a' && c <= 'z') 
		{
			if (c <= 'c') printf("2");
			else if (c <= 'f') printf("3");
			else if (c <= 'i') printf("4");
			else if (c <= 'l') printf("5");
			else if (c <= 'o') printf("6");
			else if (c <= 's') printf("7");
			else if (c <= 'v') printf("8");
			else if (c <= 'z') printf("9");	
		}
		else if (c >= 'A' && c <= 'Z')
		{
			if (c <= 'Y') putchar(c+33);
			else putchar(97);
		}
		else putchar(c);
	}
	return 0;
}

C++ :

#include<bits/stdc++.h>
using namespace std;
string a;
int flag;
int main()
{
    while(cin>>a)
    {   
        for(int i=0;i<a.size();i++)
        {
            if(a[i]>='A'&&a[i]<='Z')
            {if(char(a[i]+32)=='z')cout<<'a';else cout<<char(a[i]+33);flag=1;}
            if(a[i]>='a'&&a[i]<='z')
            {
                if(a[i]>='a'&&a[i]<='c'){cout<<2;flag=1;}
                if(a[i]>='d'&&a[i]<='f'){cout<<3;flag=1;}
                if(a[i]>='g'&&a[i]<='i'){cout<<4;flag=1;}
                if(a[i]>='j'&&a[i]<='l'){cout<<5;flag=1;}
                if(a[i]>='m'&&a[i]<='o'){cout<<6;flag=1;}
                if(a[i]>='p'&&a[i]<='s'){cout<<7;flag=1;}
                if(a[i]>='t'&&a[i]<='v'){cout<<8;flag=1;}
                if(a[i]>='w'&&a[i]<='z'){cout<<9;flag=1;}
            }
            if(a[i]=='1'){cout<<1;flag=1;}
            if(a[i]=='0'){cout<<0;flag=1;}
            if(flag==0)cout<<a[i];
            flag=0;
        }
        cout<<endl;
    }
   return 0;
}