c++ - Why does my "string mingling" method return unexpected results? -

i'm trying implement simple "string mingling" method, recursively mingles 2 strings of equal size (e.g. cat , dog becomes cdaotg -- first letter string 1, first letter string 2, , on).

my method follows:

string minglestrings(string s1, string s2, int index) {     if (index >= s1.length()) {         return "";     } else {         string mingled = "";         mingled += s1[index] + s2[index];         mingled += minglestrings(s1,s2,++index);         return mingled;     } } 

when use subscript operator on string (s1[index]), returns entire string index. specific character of string @ index, need type s1[index,index]. new me.

the problem code on line:

mingled += s1[index] + s2[index]; 

what adding codes of characters @ index, , appending result of addition string single character.

it should 2 separate operations:

mingled += s1[index]; mingled += s2[index]; 

this way append single character string each time call +=, producing result expect.

demo.