unable to work with strings

Development Tools IDE 1.x
1

Here is my code:

#include <iostream>
#include <string>

using namespace std;

int main () {
   string str1 = "Hello";
   string str2 = "World";
   string str3;
   int  len ;

   // copy str1 into str3
   str3 = str1;
   cout << "str3 : " << str3 << endl;

   // concatenates str1 and str2
   str3 = str1 + str2;
   cout << "str1 + str2 : " << str3 << endl;

   // total lenghth of str3 after concatenation
   len = str3.size();
   cout << "str3.size() :  " << len << endl;

   return 0;
}

Errors:
fatal error: iostream: No such file or directory
error compiling for board Arduino/Genuino Uno.

I am using the arduino IDE.

2

and are afaik not part of the arduino dialect. and so is int main().

But on the other hand there is String without including and
void setup() gets called once when the programm starts and then void loop() is called repeatedly

So if you want to post to the serial monitor try

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);  // Or another baudrate

}

and to print something use
Serial.print("Something") instead of

cout << "something"