C++ :: Demonstrate String Concatenation - Passing Char Array Into A Function

I have been assigned the following task and I am having difficulty in getting it to compile. The compiler is stopping at line 27 but I don't no what the error is.

The task is as follows:

Write two functions with the following function prototypes:

int my string len(char str[])
void my string cat(char dest[], char src[], int dest size)

Both functions should take zero-terminated strings as input. The first function should return the length of the string to the calling function. The second function should take a source and a destination string and the total size of the array pointed to by dest. It should then concatenated the source string onto the end of the destination string, if and only if the destination string has the capacity to store both strings. If the destination string does not have the capacity it should not alter either, print and error, and return to the calling function. Demonstrate the use both the above functions by using them in a program in which you initialise two character arrays with two strings, print out their length, print out the combined length, and print out the combined string

And this is my code so far:

/* A program to demonstrate string concatenation */

#include <iostream>
#include <string.h>
using namespace std;
int my_string_len(char str[]){ // function to calculate length of a chracter array
int len = 0;

[Code] ....