iOS 根据日期判断星座源代码

-(NSString *)getAstroWithMonth:(int)m day:(int)d{

NSString *astroString = @"魔羯水瓶双鱼白羊金牛双子巨蟹狮子处女天秤天蝎射手魔羯";
NSString *astroFormat = @"102123444543";
NSString *result;

if (m<1||m>12||d<1||d>31){
return @"错误日期格式!";
}

if(m==2 && d>29)
{
return @"错误日期格式!!";
}else if(m==4 || m==6 || m==9 || m==11) {

if (d>30) {
return @"错误日期格式!!!";
}
}

result=[NSString stringWithFormat:@"%@",[astroString substringWithRange:NSMakeRange(m*2-(d < [[astroFormat substringWithRange:NSMakeRange((m-1), 1)] intValue] - (-19))*2,2)]];

return result;
}