NSString *testStr01=@"HelloWord";        NSString *testStr02=[testStr01 substringToIndex:5];//取头（从头到哪），to不包括下标内容        NSString *testStr03=[testStr01 substringFromIndex:5];//去尾（从哪到尾），from包括下标内容        NSLog(@"testStr02:%@  testStr03:%@",testStr02,testStr03);                NSRange r={
   4,3};//取中间，从哪长度是多少        NSString*testStr04=[testStr01 substringWithRange:r];        NSLog(@"testStr04:%@",testStr04);                                //字符串的拼接        NSString *testStr05 = @"Hello";        //追加        NSString *testStr06 = [testStr05 stringByAppendingString:@"World"];        NSLog(@"testStr06:%@",testStr06);        //初始化        NSString *testStr07 = @"Hello";        NSString *testStr08 = @"World";        NSString *testStr09 = [NSString stringWithFormat:@"%@%@",testStr07,testStr08];        NSString *testStr10 = [NSString stringWithFormat:@"Hello%@",testStr08];        NSLog(@"testStr09:%@",testStr09);        NSLog(@"testStr10:%@",testStr10);                        //按指定格式(范围)追加内容        NSString *testStr11 = @"Hello";        NSString *testStr12 = [testStr11 stringByAppendingFormat:@"%@%@",@"World",@"123"];        NSLog(@"testStr12:%@",testStr12);                        //替换        NSString *testStr13 = @"www.kyle.com.cn";        NSString *testStr14 = [testStr13 stringByReplacingCharactersInRange:NSMakeRange(4, 6) withString:@"163"];        NSLog(@"testStr14:%@",testStr14);                        //编码集        //参数 文件的路径 不包括文件名        NSString *path = @"/Users/apple/Desktop";        //path = [path stringByAppendingString:@"/test.txt"];        path = [path stringByAppendingString:@"/test.rtf"];        //把文件中的内容 读取到字符串中        //NSString *str20 = [[NSString alloc]initWithContentsOfFile:path];                NSString *testStr15 = [[NSString alloc]initWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];                NSLog(@"testStr15:%@",testStr15);                        NSString* use=@"fcp";        NSString* use1=@"fcp";                NSString*password=@"123";        NSString*password1=@"123";        if ([use isEqualToString:use1]&&[password isEqualToString:password1]) {            NSLog(@"登陆成功");        }        else{            NSLog(@"登陆失败");        }