how to display looping result

Hi, i need to write one program which if i < 5, it will callFunction to add one character; so it will loop for 5 times for each. And the result display in label.text have to look like a,b,c,d,e; can anyone teach me on how to display the result in this case? as my coding will keep overwrite the previour character each time it loop. Thank for helping..
    {
                 for (int i = 0; i < 5; i++)
                    label.text = (CallFunction(j));
            } 
...