NSMutableString

#import <Foundation/Foundation.h>

#pragma mark - 创建可变字符串
void stringCreate(){
    NSMutableString *str=[[NSMutableString alloc] initWithCapacity:10];//预分配是个空间,提高效率
    //设置字符串的内容
    [str setString:@"123"];
    //连接字符串
    [str appendFormat:@"age is %i and height is %.2f",27,175.5f];
    [str appendString:@"添加结束"];
    //字符串替换
    NSRange range=[str rangeOfString:@"age"]; //找到当前字符串的位置
    [str replaceCharactersInRange:range withString:@"年龄"];  //替换字符串
    //插入字符串
    [str insertString:@"我是插入的字符串" atIndex:2];
    NSLog(@"可变字符串是:%@",str);
    [str release];//释放对象
    
}

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

    @autoreleasepool {
        
        stringCreate();
    }
    return 0;
}

结果：

2013-08-02 15:29:58.909 NSMutableString[1145:303] 可变字符串是:12我是插入的字符串3年龄 is 27 and height is 175.50添加结束