数据类型转换

            //1.值类型的转换注意大小(隐式转换和强制转换)long chang = 56595959;
            int int4 = 23;
            chang = int4;

            int4 = (int)chang;

            //2.引用类型的强制转换
            Animal a = new Animal();
            Dog d = null;
            //d = (Dog)a;

            //2.1 引用类型的隐式转换
            a = d;

            //数据类型中引用类型string的问题
            string aa = "abc";
            aa = "cde";
            string bb = "def";
            aa += bb;      

            //如果要拼接大量的字符串，就使用StringBuilder,比如拼接SQL
            StringBuilder sb = new StringBuilder("a");
            sb.Append("b");
            sb.Append("c");
            sb.Append("d");
            string jieguo = sb.ToString();

            //var names = [];
            //names.push("a");
            //names.push("b");
            //names.push("c");
            //var nj = names.join('');