String
void main(){
String str1 ='hello';
String str2 ='''hello dart''';
String str3 ='hello \n dart';
String str4 =r'hello \n dart';
String str5 ='Go go go';
int a = 1;
int b = 2;
print('a+b = ${a + b}');
print(str2);
print(str3);
print(str4);
print(str5 +'qianqian');
print(str5 *5);
print(str4 == str5);
print(str5[0]);
print(str5.length);
print(str5.isEmpty);
print(str5.contains('G'));//是否包含
print(str5.substring(0,2));//截取前两个字符
print(str5.startsWith('a'));//是不是以a开头的
print(str5.endsWith('o'));//是不是以a结尾的
var list = str5.split(" ");//分割字符串
print(list);
}