Changing dates

ITmajor has asked for the wisdom of the Perl Monks concerning the following question:

I am having a problem with my code changing to the correct month and day. When it is the end of the month the program does not go to the beginning of the next. For example, instead of changing from May 31 to June 1, it will change to June 30. Am I missing somnething? This is the code I have:

if ($start_month == "04"||"06"||"09"||"11"){        
    if ($start_day == 30){                
        $start_day = sprintf "%0.2d", $start_day+ 1; 
        $start_day == 01;            
    }
else {$start_day = sprintf "%0.2d", $start_day + 1}; 
}
elsif ($start_month == "01"||"03"||"05"||"07"||"08"||"10"||"12"){    
    if ($start_month == 12 && $start_day == 31){    
        $start_year ++;                
        $start_month == 01;            
        $start_day == 01;            
    }
    elsif($start_day == 31){                
        $start_day = sprintf "%0.2d", $start_day+ 1; 
        $start_day == 01;            
    }     
    else {$start_day = sprintf "%0.2d", $start_day+ 1};
}
else {
    if ($start_day == 28){                
        $start_month == 03;            
        $start_day == 01;            
    }     
    else {$start_day = sprintf "%0.2d", $start_day+ 1}; 
}
[download]

Comment on Changing dates Download Code

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Re: Changing dates by moritz (Cardinal) on Dec 17, 2008 at 18:52 UTC
Whenever you do date calculations manually, you are making a big mistake. They are harder than you think, and you never get them quite right. Thankfully there are many well tested modules on CPAN for that, for example DateTime, Date::Manip, Date::Calc. If you just want to deal with days, and never with times, Date::Simple can really be recommended, it uses a super-easy interfaces probably does exactly what you want (whatever it is) very easily.	[reply]
Re: Changing dates by toolic (Bishop) on Dec 17, 2008 at 18:49 UTC
Instead of: `if ($start_month == "04"\|\|"06"\|\|"09"\|\|"11"){` [download] You probably really want: `if ($start_month eq "04" \|\| $start_month eq "06" \|\| $start_month eq "0 +9" \|\| $start_month eq "11"){` [download] or even (using grep and "eq" for string comparison): `if (grep {$start_month eq $_ } qw(04 06 09 11)) {` [download] or a hash. But you probably really should use a CPAN module for this.	[reply] [d/l] [select]
Re: Changing dates by johngg (Canon) on Dec 17, 2008 at 18:56 UTC
You may find this recent post of interest. Cheers, JohnGG	[reply]
Re: Changing dates by MidLifeXis (Monsignor) on Dec 17, 2008 at 18:54 UTC
~~Did you run this through `use strict; use warnings;`?~~ Check the precedence of your operators. This code: `if ($foo == "A"\|\|"B"\|\|"C")` is actually the same as `if (($foo == "A") \|\| ("B") \|\| ("C"))` which should reduce to `if (1)`. Also, you have a `$start_day == 01` in every section. `==` is a comparison, `=` is an assignment. --MidLifeXis	[reply] [d/l] [select]
Re^2: Changing dates by chromatic (Archbishop) on Dec 17, 2008 at 22:23 UTC
Did you run this through `use strict; use warnings;`? How would either help in this case? I don't get any errors or warnings about this construct with Perl 5.8.8 or 5.10.0.	[reply] [d/l]
Re^3: Changing dates by MidLifeXis (Monsignor) on Dec 17, 2008 at 22:47 UTC
D'oh. Must be the ass-u-me thing. Thought that the `$var == 01` at the end of the if blocks would trigger a "useless" something or another. My mistake. --MidLifeXis	[reply] [d/l]
Re^2: Changing dates by ITmajor (Beadle) on Dec 18, 2008 at 18:56 UTC
Also, you have a $start_day == 01 in every section. == is a comparison, = is an assignment. thanks for pointing that out.....problem solved	[reply]
Re: Changing dates by DStaal (Chaplain) on Dec 17, 2008 at 18:54 UTC
Coding it yourself is nearly always the wrong way to handle date math. Check out Date::Calc and the DateTime modules If you really must do this yourself, read through this recent node: Increment through date range by day with only standard modules. for ideas on how to do this correctly.	[reply]
Re: Changing dates by imrags (Monk) on Dec 18, 2008 at 06:42 UTC
I've used Date::Pcalc to modify dates and I really like it... It is very useful to add/subtract/calculate dates... Raghu	[reply]