z3

#include <iostream>
#include <stdlib.h>
#include <ctime>
using namespace std;

int main()
{
   string incoming,output="";

   do{
   cout<<"Podaj ciag znakow (max 20): ";
   cin>>incoming;
   cout<<endl;
   }while(sizeof(incoming)<=20);

   for(int i=0;i<incoming.length();i++) {
    switch(incoming[i]){
    case 'A'...'Z': output+=incoming[i]+32; break;
    case 'a'...'z': output+=incoming[i]-32; break;
    default: output+= '_';
    }
   }
    cout<<output;
    return 0;
}