C/C++ :: Creating Username From Name

I'm trying to create a simple program that reads in the user's first name, middle name, and last name. Then inside of the userName function, I want it to only take the first letter of firstName, first letter of middleName, and then just output the full last name. So for example: if your name was John Kevin Smith, it would output jksmith. I'm having a lot of compile issues due to the pointers. I have to use the function in this code, so the pointers are needed.

#include <stdio.h>
#include <string.h>
int main() {
char userName (char firstName[12], char middleName[12], char lastName[12], char firstInit[1], char secondInit[1]);
char firstName[12];
char middleName[12];
char lastName[12];
char firstInit[1];

[Code] ....