You have to pay attention: without break; the switch executes all code after finding a match (for example: if imput is 8 your function will return "Eight" and then "Nine" because a break; is missing)!

C translaton doesn´t seem to work.

In C the longest RandomTest returs an error, although my solution is the correct number. (probably it´s buffer overflow but I don´t know what buffer overflow is, hope that´s not the issue here)