First of all a few problems:
1. For strlen to work, you should include string.h or cstring depending on your compiler.
2. Your method declaration for combine should match at both places (return type of function should be void at last).
Now, the actually error, we call it Copy-Paste Error. In the last final loop you are iterating your array till you find a space, which is not necessary in each case. Rather you should look for a End of String '\0'. So change your last while loop to:
while (C[final]!= '\0')
It works for me after doing this.
If input is: Manoj Kumar Singh
Output is: M. K. Singh
I hope this is what you expected.