What type of data conversion is taking place, implicit or explicit?

Question

1) int a, b;
c = (float)(a + b);

2) char a; int , c;
d = (a + b + c);

Answer 1

1.) explicit
2.) implicit // guessing b is an int as it looks to be omitted from the declaration

Answer 2

Actually, I forgot to declare b. :P
Thanks for your time and answer. :D