Update coinchange.cpp

[md-shamim-ahmad]

I have updated some code in this solution code and request you to merge this solution code.

Fixes issue:

If the given input amount is greater than 100 then previous solution code give us a runtime error. In my solution code, I fixed this problem.

If we look at the previous solution code then we will see that, Memory complexity of that solution is static. But in my case the memory complexity is dynamic.

Changes:

I have changed a little bit of this code so that the format of this code looking better.