可变字符串

        //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);