How to print out ASCII character given number in C++?

I am calculating an integer based on an barcode image. The int will have a value between 1 (2^0) and 256(2^8). I am trying to create a string of characters, each represented by the int which I get from evaluating an individual column of a barcode.

I don't know how to convert an int to a string and then append that string to the end of another string (an empty one initially). I have tried the following (where col_sum is my integer):

string temp_str, full_temp_str;

stringstream ss;

char temp_char;

temp_char = (char)col_sum;

ss << temp_char;

ss >> temp_str;

full_temp_str.append(temp_str);