OC之NSMutableString

```objective-c
#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {

@autoreleasepool {

//NSMutableString(可变字符串)是NSString的子类

//声明可以字符串并初始化

//定义长度为并不是最大长度,是为了性能

NSMutableString *str = [[NSMutableString alloc] initWithCapacity:10];

[str setString:@"0123456789abc"];

NSLog(@"%@",str); //输出 0123456789abc

//追加字符串

[str appendString:@"def"];

NSLog(@"%@",str); //输出 0123456789abcdef

[str appendFormat:@"%d",1];

NSLog(@"%@",str); //输出 0123456789abcdef1

//替换字符串

NSMutableString *str1 = [[NSMutableString alloc] initWithCapacity:10];

[str1 setString:@"hello word"];

NSRange range = [str1 rangeOfString:@"word"];

[str1 replaceCharactersInRange:range withString:@"世界"];

NSLog(@"%@",str1); //输出 hello 世界

//插入字符串

NSMutableString *str2 = [[NSMutableString alloc] initWithCapacity:10];

[str2 setString:@"中国民很行"];

[str2 insertString:@"人" atIndex:2];

NSLog(@"%@",str2); //输出 中国人民很行

//删除字符串

NSRange range1 = NSMakeRange(0, 2);

[str2 deleteCharactersInRange:range1];

NSLog(@"%@",str2); //输出 人民很行

}

return 0;

}
```