Аnalog of \ifodd condition for verification if page number is equal to some constant

Question

I have a great example of using \ifodd condition if \makeatletter environment showed by @Symbol 1.

\begin{document}
\makeatletter
\newbox\LT@oddhead
\newbox\LT@evenhead
\def\endoddhead{\LT@end@hd@ft\LT@oddhead}
\def\endevenhead{\LT@end@hd@ft\LT@evenhead}
\def\LT@head{\ifodd\c@page\LT@oddhead\else\LT@evenhead}
\makeatother
\begin{landscape}\small\begin{longtabu}to\linewidth{lll XX XXXXX}
    \caption*{ Long caption of a long table}\\\toprule1&2&3&4&5&6&7&8\\\midrule\endfirsthead
    \caption*{ (Cont) Long caption of a long table }\\\toprule1&2&3&4&5&6&7&8\\\midrule\endoddhead
    \toprule1&2&3&4&5&6&7&8\\\midrule\endevenhead

I want to add one more statement to check if pagenumber is equal to some constant. For example:

\def\LT@head{\ifeq\c@page={some constant}\{some stuff}\else\LT@head}

But I can't find analoge for \ifodd command in \makeatletter environment. Any ideas?

EDIT: add minimal working example EDIT2: reduced MWE and added @-sign before someconstant. If I will uncomment line with \ifnum compiler won't make a pdf. The warning message is ! Missing number, treated as zero.. I'm still confused.

\documentclass[a4paper, 10pt, oneside,hidelinks]{book} 
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}
\usepackage{booktabs}
\usepackage{lscape}
\usepackage{tabu}
\usepackage{longtable}



\begin{document}
\makeatletter
\newbox\LT@oddhead
\newbox\LT@evenhead
\newbox\LT@endhead
\newcommand{\@someconstant}{2}
\newcommand{\Endd}{End}
\def\endoddhead{\LT@end@hd@ft\LT@oddhead}
\def\endevenhead{\LT@end@hd@ft\LT@evenhead}
\def\endendhead{\LT@end@hd@ft\LT@endhead}
\def\LT@head{\ifodd\c@page\LT@oddhead\else\LT@evenhead}
%\def\LT@head{\ifnum\c@page=\@someconstant\relax\Endd\else\LT@head\fi}
\makeatother



\begin{landscape}
  \small
\begin{longtabu} to \linewidth{ lll XX  XXXXX}

\caption*{ Long caption of a long table}\\\toprule1&2&3&4&5&6&7&8\\\midrule\endfirsthead
    \caption*{ (Cont) Long caption of a long table }\\\toprule1&2&3&4&5&6&7&8\\\midrule\endoddhead
    \toprule1&2&3&4&5&6&7&8\\\midrule\endevenhead
    End\\\endendhead


  \bottomrule
  \endfoot

  \bottomrule
  \endlastfoot




1-й

 & Длина, мм & Самцы & —
 & 85,1--104,0 93,7 (6) & 100,6 (1) & —
 & —
 & —
 & —
 \\ &  & Самки & —
 & 92,1--105,8 97,6 (4) & 137,6 (1) & —
 & —
 & —
 & —
 \\ 
 &  & juv & 43,6–82,0 53,3 (20) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 2,3--4,2 \linebreak2,8 (6) & 3,2 (1) & —
 & —
 & —
 & —
 \\ 
 &  & Самки & —
 & 2,2--3,6\linebreak 2,7 (4) & 7,9 (1) & —
 & —
 & —
 & —
 \\ 
 &  & juv & 0,2--1,8\linebreak 0,4 (20) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
\\

2-й & Длина, мм & Самцы & —
 & 72,0--114,0
93,6 (16) & 104,3--132,3
113,4 (4) & 121,5--178,2
139,3 (9) & 
158,9 (1) & 193,7--212,7
175,6 (3) & —
 \\ 
 &  & Самки & —
 & 77,5--110,4
95,2 (7) & 110,4--131,3
117,6 (4) & 167,8 (1) & —
 & 182,9 (1) & —
 \\ 
 &  & juv & 45,1--86,9
51,9 (40) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,1--5,1 \linebreak 2,7 (16) & 3,7--5,5 \linebreak 4,3  (4) &
 5,1--15,0\linebreak  9,2 (9) 
 & 17,0 (1) & 21,0--30,0 26,3 (3) & —
 \\ 
 &  & Самки & —
 & 1,5--4,7
\linebreak2,8 (7) & 4,0--6,1
\linebreak5,1 (4) & 15,0 (1) & —
 & 34,0 (1) & —
 \\ 
 &  & juv & 0,2--1,3
\linebreak0,4 (40) & —
 & —
 & —
 & —
 & —
 & —
 \\ 

\\

3-й & Длина, мм & Самцы & —
 & 85,8--114,6
100,4 (7) & 113,7--131,2
118,3 (5) & 124,0--172,7
148,3 (2) & 144,6  (1)
 & —
 & 181,7--184,0
182,8 (2) \\ 
 &  & Самки & —
 & 84,7--115,7
98,0 (9) & 109,1--156,4
133,3 (3) & 106,9--167,1
140,0 (3) & 159,3 (1) & 222,6 (1) & 170,2 (1) \\ 
 &  & juv & 42,3--90,4
61,0 (26) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 2,1--5,2
\linebreak3,7 (7) & 4,5--10,0
\linebreak5,8 (5) & 7,6--19,0
\linebreak13,3 (2) & 11,0 (1) & —
 & 23,5--24,9
24,2 (2) \\ 
 &  & Самки & —
 & 2,0--5,9
\linebreak3,5 (9) & 4,9--14,0
\linebreak9,7 (3) & 4,5--21,0
\linebreak12,5 (3) & 15,0 (1) & 39,0 (1) & 18,0 (1) \\ 
 &  & juv & 0,3--2,6
\linebreak0,9 (26) & —
 & —
 & —
 & —
 & —
 & —
 \\ 

\\

4-й & Длина, мм & Самцы & —
 & 77,6--112,0
92,7 (14) & 115,2--140,2
127,7 (2) & 135,2 (1) & 146,1--181,1
159,9 (3) & 157,9 (1) & 175,4--244,7
210,0 (2) \\ 
 &  & Самки & —
 & 88,0--113,7
99,1 (4) & 105,0--157,1
135,4 (6) & 123,0--174,3
141,3 (6) & 134,2--182,3
160,1 (3) & 181,6--187,0
183,4 (3) & —
 \\ 
 &  & juv & 43,9--81,0
52,0 (19) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,2--5,0
\linebreak2,7 (14) & 5,0--12,0
\linebreak8,5 (2) & 10,9 (1) & 12,0--23,0
\linebreak16,6 (3) & 13,4 (1) & 17,0 (1) \\ 
 &  & Самки & —
 & 2,0--6,0
\linebreak3,2 (4) & 4,3--17,0
\linebreak9,3 (6) & 7,0--26,0
\linebreak13,0 (6) & 7,0--19,8
\linebreak14,4 (3) & 20,0--36,0
\linebreak25,3 (3) & —
 \\ 
 &  & juv & 0,2--2,3
\linebreak0,5 (19) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
\\


5-й & Длина, мм & Самцы & —
 & 71,7--108,2
\linebreak91,3 (32) & 87,3--140,0
\linebreak110,6 (39) & 105,6--149,4
\linebreak126,8 (7) & 130,4--160,9
\linebreak149,6 (5) & 166,2 (1) & —
 \\ 
 &  & Самки & —
 & 80,2--105,4
\linebreak93,2 (30) & 93,6--152,9
\linebreak114,0 (48) & 123,0--147,1
\linebreak136,3 (12) & 144,2--147,0
\linebreak145,6 (2) & 140,7--179,6
\linebreak160,1 (2) & —
 \\ 
 &  & juv & 43,0--99,5
\linebreak73,1(47) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,0--4,7
\linebreak2,6 (32) & 1,7--13,0
\linebreak4,6 (39) & 3,6--15,0
\linebreak8,37(7) & 9,1--21,0
\linebreak14,9 (5) & 11,6 (1) & —
 \\ 
 &  & Самки & —
 & 1,7--4,7
\linebreak2,9 (30) & 2,0--17,0
\linebreak5,5 (48) & 7,9--15,4
\linebreak10,9 (12) & 9,9--13,0
\linebreak11,4 (2) & 12,3--28,0
\linebreak20,1 (2) & —
 \\ 
 &  & juv & 0,2--4,2
\linebreak1,4 (47) & —
 & —
 & —
 & —
 & —
 & \multicolumn{1}{l}{—
} \\ 
 &  &  &  &  &  &  &  &  &  \\ 
\\


6-й & Длина, мм & Самцы & —
 & 61,0--147,4
\linebreak98,2 (19) & 104,1--166,3
\linebreak120,4 (27) & 119,1--189,3
\linebreak147,0 (12) & 139,0--175,4
\linebreak157,2 (3) & 176,6--215,0
\linebreak195,8 (2) & 199,1--267,0
\linebreak246,4 (5) \\ 
 &  & Самки & —
 & 78,2--139,6
\linebreak99,1 (15) & 93,3--162,4
\linebreak122,3 (23) & 119,0--177,0
\linebreak145,6 (6) & 145,8--169,7
\linebreak158,9 (4) & 203,6 (1) & 212,9 (1) \\ 
 &  & juv & 44,0--96,3
\linebreak64,4 (35) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,3--13,0
\linebreak5,0 (15) & 2,7--14,0
\linebreak5,9 (27) & 6,5--24,0
\linebreak12,0 (12) & 9,0--9,8
\linebreak9,4 (2) & 18,0--38,0
\linebreak28,0  (2) & 19,6--73,0
\linebreak49,7 (5) \\ 
 &  & Самки & —
 & 1,6--11,0
\linebreak4,4 (12) & 1,8--13,0
\linebreak6,3 (23) & 5,6--16,0
\linebreak11,3 (5) & 10,7--18,0
\linebreak13,9 (4) & 34,0 (1) & 36,0 (1) \\ 
 &  & juv & 0,2--3,0
\linebreak1,3 (35) & —
 & —
 & —
 & —
 & —
 & —
 \\ 

\\

7-й & Длина, мм & Самцы & —
 & 69,6--131,3,5
\linebreak93,4 (39) & 83,5--159,1
\linebreak116,4 (41) & 105,4--181,8
\linebreak138,8 (14) & 132,0--168,0
\linebreak153,7 (5) & 134,9--178,9
\linebreak156,9 (2) & 193,5 (1) \\ 
 &  & Самки & —
 & 64,9--133,0
\linebreak88,2 (31) & 83,3--169,1
\linebreak121,6 (39) & 95,2--168,4
\linebreak136,9 (20) & 136,0--183,8
\linebreak158,8 (5) & 163,1--202,0
\linebreak177,1 (3) & 200,0 (1) \\ 
 &  & juv & 39,1--93,1
\linebreak61,3 (150) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,0--9,0
\linebreak3,0 (39) & 1,8--17,0
\linebreak6,3 (41) & 4,1--34,0
\linebreak12,1 (14) & 8,4--21,7
\linebreak15,2 (5) & 9,1--22,0
\linebreak15,5 (2) & 39,0 (1) \\ 
 &  & Самки & — & 1,0--8,7
\linebreak2,3 (31) & 1,7--22,0
\linebreak7,6 (39) & 4,0--24,0
\linebreak11,3 (20) & 9,0--26,0
\linebreak17,6 (5) & 15,0--39,0
\linebreak23,5 (3) & 51,0 (1)
 \\ 
 &  & juv & 0,1--3,5
\linebreak0,8(150) & —
 & —
 & —
 & —
 & —
 & —
 \\
\\ 

Общее & Длина, мм & Самцы & —
 & 61,0--147,4
\linebreak93,6 (133) & 83,5--166,3
\linebreak115,5 (119) & 105,4--189,3
\linebreak140,4 (45) & 130,4--181,1
\linebreak153,9 (18) & 134,9--215,0
\linebreak178,9 (9) & 175,4--267,0
\linebreak221,1 (10) \\ 
 &  & Самки & —
 & 64,9--139,6
\linebreak93,5 (100) & 83,3--169,1
\linebreak119,7 (124) & 95,2--177,0
\linebreak139,1 (48) & 134,2--183,8
\linebreak157,4 (15) & 140,7--222,6
\linebreak182,8 (11) & 170,2--212,9
\linebreak194,4 (3) \\ 
 &  & juv & 39,1--99,5
\linebreak61,8 (337) & —
 & —
 & —
 & —
 & —
 & —
 \\ 
 & Масса, г & Самцы & —
 & 1,0--13,0
\linebreak3,1 (129) & 1,7--17,0
\linebreak5,8 (119) & 3,6 -34,0
\linebreak11,0  (45) & 8,4--23,0
\linebreak14,5 (17) & 9,1--38,0
\linebreak21,3 (9) & 17,0--73,0
\linebreak39,4 (9) \\ 
 &  & Самки & —
 & 1,0--11,0
\linebreak2,9  (97) & 1,7--22,0
\linebreak6,6  (124) & 4,0--26,0
\linebreak11,5 (47) & 7,0--26,0
\linebreak14,8 (15) & 12,3--39,0
\linebreak26,7 (11) & 18,5--51,0
\linebreak35,1 (3) \\ 
 &  & juv & 0,1--4,2
\linebreak0,9 (337) & —
 & —
 & —
 & —
 & —
 & —
 \\ 

\end{longtabu}
\end{landscape}


\end{document}

Answer 1

This answer is more general in terms of your question: How to check for the page number being something specific; not just odd?

Use refcount.

Why? When you're talking about page numbers you have to remember that TeX's page builder is asynchronous, and you could end up testing for a page number that you're actually not on. As such, using references is the best way to achieve the correct page number. And when you're wanting to compare reference counters, refcount does the job.

\documentclass{article}
\usepackage{refcount,lipsum}
\begin{document}
Label \verb|abc| is on page~\pageref{abc}.
\ifnum\getpagerefnumber{abc}=5
  True
\else
  False
\fi

\lipsum[1-25]
\label{abc}
\lipsum[26-50]
\end{document}

After the first compilation, the reference is not yet available, and \getpagerefnumber{<label>} defaults to 0. So for the correct output, you need compile at least twice on the first go, after which the references would just have to be settled in order for the condition to be evaluated properly. Regardless, LaTeX will warn of any reference issues, if they exist.