//1.创建可变字符串        //NSMutableString 继承自 NSString        //NSMutableString 用油NSString所有的属性以及方法//        NSMutableString * muStr = [[NSMutableString alloc] init];        NSMutableString * muStr = [[NSMutableString alloc] initWithCapacity:0];                //是初始化字符串内容        [muStr setString:@"www"];                NSLog(@"mustr %p",muStr);                //动态的给字符串末尾追加新值        [muStr appendString:@".cn"];                //在指定的索引位置,插入字符串        [muStr insertString:@".itcast" atIndex:3];                //删除指定范围的字符串        //你要删除的长度,一定不能够超出字符串的的长度,导致异常Range or index out of bounds        NSRange range = {3,7};//        [muStr deleteCharactersInRange:range];                [muStr replaceCharactersInRange:range withString:@"传智播客"];                NSLog(@"muStr %@",muStr);