global str1 = "Hello ";

string string_concat (string str1, string str2) {
  var arr1 = array_of_string (str1);
  var arr2 = array_of_string (str2);
  var len1 = length_of_array (arr1);
  var len2 = length_of_array (arr2);
  var arr3 = new int[len1+len2];
  var i = 0;
  for(var j=0; j<len1; j=j+1;) {
    arr3[i] = arr1[j];
    i=i+1; 
  }
  for(var j=0; j<len2; j=j+1;) {
    arr3[i] = arr2[j];
    i=i+1;
  }
  return string_of_array (arr3);  
}

int program (int argc, string[] argv) {
  var str2 = "world!";
  print_string (string_concat (str1, str2));
  return 0;
}