concat variable in string dart code example

Example: dart concatenate string

String a = 'a';
String b = 'b';

var c1 = a + b; 	// + operator
var c2 = '$a$b'; 	// string interpolation	(prefered method)
var c3 = 'a' 'b'; 	// string literals separated only by whitespace are concatenated
var c4 = 'abcdefgh abcdefgh abcdefgh abcdefgh' 
         'abcdefgh abcdefgh abcdefgh abcdefgh';