c++11 - Variable initialization guidelines in C++ -

which guidelines initialize variables in c++? there many ways initialize variable in c++. 3 ways familiar following:

1) int a=3;

2) int a(3);

3) int a{3}; // valid c++11 & later

which best approach? why 2nd way int a(3); not seen & not used in c++ programs?
thanks.

the first 2 initializations have same effect. guess people prefer first option on second 1 because looks more natural.

the third option has different rules: forbids narrowing conversion. while can do

int = .3; 

and int equals zero,

int {.3}; 

will compile time error. brace initializer has advantage stops doing such conversions on accident , forces explicitly state intend if really want narrowing conversion.