How to convert integers to characters?

Is there any functions to convert integers to characters?

For example:
real::a=123.4 ! a is a real number
character(len=30)::b ! b is a character
!How can I convert a to b as a character, i.e. b would be 123.4, but b
is a character.

Moreover, is there any other functions can reverse the conversion?
i.e. from characters to numbers.

character(len=30)::b="123.4"
real::a

how can I assign 123.4 to a as a real number?

Many thanks!

.