Пример работы со строками

#include <conio.h>
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
 
char* Read(char* message)
{
  int ch, str_size = 0;
  char * str = (char *) calloc(str_size, sizeof(char));
  cout<<message;
  while ((ch = getchar()) != '\n')
  {
    str = (char *) realloc(str, ++str_size);
    str[ str_size - 1 ] = (char) ch;
  }
  str[ ++str_size - 1 ] = '\0';
  return str;
}
 
void main()
{
  char* Str1 = Read("Enter first string: ");
  char* Str2 = Read("Enter second string: ");
  char* Str3 = Read("Enter third string: ");
 
  int charcount = 0;
  char* Res = NULL;
  for(int i = 0; i < 3;i++)
  {
    for(int j = 0; j < 5;j++)
    {
      if(Str1[i] == Str2[j])
      {
        for(int k = 0; k < 4;k++)
        {
          if(Str2[j] == Str3[k])
          {
            Res = (char*)realloc(Res, ++charcount*sizeof(*Res));
            Res[charcount-1] = Str3[k];
          }
        }
      }
    }
  }
  Res = (char*)realloc(Res, ++charcount*sizeof(*Res));
  Res[charcount-1] = '\0';
 
  cout<<Res;
  getch();
}