How To Make A Password Generator In C++

i am new to c++ and this is a interesting thing ok now this is a preview of my code

ok now heres the code

#include<iostream>
#include<stdlib.h>
#include<time.h>
#include<string.h>
using namespace std;
int main()
{
   int length,x,str,j=0,answ;
   char pass[255],s[255],
   alphan[]="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
   alph[]="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ",
   num[]="0123456789";
   cout<<"Choose the password characters: \n1-Alphanumerics (a-z,A-Z,0-9) \n2-Only letters \n3-Only numbers \n4-Manually inserted characters\nMode:";cin>>answ;
   if(answ==4)
   {
      cout<<"Enter the characters desired WITHOUT SPACE: ";cin>>s;
      str=strlen(s);
   }
   cout<<"Password length=";cin>>length;
   srand(time(NULL));
   switch(answ)
   {
      case 1:{while(length--)
                  {
                     x=rand()%62;
                     pass[j++]=alphan[x];
                  }
               } break;
      case 2:{while(length--)
                  {
                     x=rand()%52;
                     pass[j++]=alph[x];
                  }
               } break;
      case 3:{while(length--)
                  {
                     x=rand()%10;
                     pass[j++]=num[x];
                  }
               } break;
      case 4:{while(length--)
                  {
                     x=rand()%str;
                     pass[j++]=s[x];
                  }
               } break;
   }

cout<<"Password: ";
   for(int i=0;i<j;i++)
      cout<<pass[i];
   return 0;
}

preview -