IOS 数组排序、转字符、字符拼接、corn表示式用法

最终目的是达到corn表达式的目的。

1. 数组排序:NSArray *week = {3,2,4};      weeks = [weeks sortedArrayUsingSelector:@selector(compare:)];

2. 数组转字符串： NSString *strWeek；  strWeek = [weeks componentsJoinedByString:@","];

3. 字符拼接： NSString *corn =  [@"0 "stringByAppendingFormat:@"%@%@%@%@%@", currentMinute,@" ",currentHour,@" ? * ",strWeek];