But if it I don't allocate the memory, it causes a memory access error

My solution for C, sets the IPv4 to the right value with a null value to end it. However when the test is run the intput is shown as a load of random sysmbols such as '@@@@@@@@@@@@@@@@!@@@' etc

My code in C, passes all the sample tests, but when i try to attempt it with the main tests it fails. On the tests screen it says the nums array is just an array with differnet symbols and no numbers.
My code is making a char array with the right format, and when it returns in the sample tests its correct. But in the main tests nothing gets returned.

In C. I have wrote to the output variable. When I print it, it holds the correct information but the tests say the output variable is empty.