挑战:如何将一系列数字转换成英文可读的列表

听着,妈妈,没有如果!

NSString *seps[] = {@" and ",@"",@", ",nil,nil,@", "}, *o = @".", *sep = o;
for ( NSNumber *n in [arr reverseObjectEnumerator] ) {
   o = [NSString stringWithFormat:@"%@%@%@",n,sep = seps[[sep length]],o];
}

NSLog(@"out: %@",o);

out: 5, 7, 12 and 33.

但为什么呢?

这是一个可以理解的版本,没有“巨大的if/else构造”

NSString *out = @"";  // no numbers = empty string
NSString *sep = @"."; // the separator first used is actually the ending "."
for ( NSNumber *n in [arr reverseObjectEnumerator] )
{
    out = [NSString stringWithFormat:@"%@%@%@",n,sep,out];
    if ( [sep isEqualToString:@"."] ) // was the separator the ending "." ?
    {
        sep = @" and "; // if so, put in the last separator " and "
    } else {
        sep = @", ";    // otherwise, use separator ", "
    }
}

0 elements: ""        (i.e. empty)
1 element:  "33."
2 elements: "12 and 33."
3 elements: "7, 12 and 33."

NSArray *numbers = [NSArray arrayWithObjects:[NSNumber numberWithInt:5],
                          [NSNumber numberWithInt:7],
                          [NSNumber numberWithInt:12],
                          [NSNumber numberWithInt:33], nil];
NSArray *first = [numbers subarrayWithRange:NSMakeRange(0, [numbers count]-1)];
NSString *joined = [[first componentsJoinedByString:@", "] stringByAppendingFormat:(([first count] > 0) ? @"and %@" : @"%@"), [numbers lastObject]];