multiplicaciones para niños

mult.tex

\documentclass[12pt,a4paper]{article}
\usepackage[margin=0.8in]{geometry}
\usepackage{amsmath}
\usepackage{array}
\usepackage{tikz}
\usetikzlibrary{calc}

\pagestyle{empty}

% ---- unified N×M renderer (tight alignment) ----
\newcommand{\boxw}{0.8}  % cm
\newcommand{\boxh}{1.0}  % cm

% lengths / digits (pure TeX)
\newcommand{\NumberLen}[2]{%
  \begingroup
  \count0=#1\relax \ifnum\count0<0 \multiply\count0 by -1\fi
  \count2=0\relax
  \ifnum\count0=0 \count2=1\else
    \loop \advance\count2 by 1 \divide\count0 by 10 \ifnum\count0>0 \repeat
  \fi
  \xdef#2{\the\count2}%
  \endgroup
}
\newcommand{\ExtractDigit}[3]{%
  \begingroup
  \count20=#1\relax \count30=#2\relax \count22=1
  \loop\ifnum\count30>0 \multiply\count22 by 10 \advance\count30 by -1\repeat
  \divide\count20 by \count22
  \count24=\count20 \divide\count24 by 10 \multiply\count24 by 10
  \advance\count20 by -\count24
  \xdef#3{\the\count20}%
  \endgroup
}

% Draw N dotted boxes with the **right edge** at (X,Y), extending left
\newcommand{\PlaceBoxes}[3]{% N, X, Y  (TikZ calc is loaded)
  \pgfmathtruncatemacro{\N}{#1}
  \ifnum\N>0
    \pgfmathtruncatemacro{\NmOne}{\N-1}
    \foreach \i in {0,...,\NmOne}{%
      \draw[dotted,thick] ($(#2,#3)+(-\i,0)$) rectangle ++(-1,-1);
    }%
  \fi
}

% Unified problem macro (3rd arg ignored)
\newcommand{\multproblem}[2]{%
  \begin{minipage}[t]{0.48\textwidth}
  %we need to anchor the top left of this minipage:
  \text{ }
  \begin{center}
  \begin{tikzpicture}[every node/.style={font=\Huge}, x=\boxw cm, y=\boxh cm]
    \def\A{#1}\def\B{#2}%
    \NumberLen{\A}{\alen}\NumberLen{\B}{\blen}%
    \edef\RES{\number\numexpr \A*\B\relax}%
    \NumberLen{\RES}{\slen}%
    \count51=\alen\relax \count52=\blen\relax
    \ifnum\count51>\count52 \edef\maxab{\alen}\else\edef\maxab{\blen}\fi

    % --- Tunables for spacing (in box-height units) ---
    \def\ruleY{-2.0}     % y of the first rule
    \def\gap{0.12}       % tiny gap from rule to boxes
    \def\rowskip{0.12}   % tiny gap between rows of boxes
    \def\sumbuffer{0.20} % tiny gap above the sum rule

    % Top numbers, right-aligned to the result width
    \node[anchor=east] at (\slen,  0.00) {#1};
    \node[anchor=east] at (\slen, -1.20) {$\times$ #2};

    % First rule: width = max(len A, len B)
    \pgfmathtruncatemacro{\ruleStart}{\slen - \maxab}
    \draw[thick] (\ruleStart, \ruleY) -- (\slen, \ruleY);

    % Partial products (one row per digit of B, right->left)
    \count50=\blen \advance\count50 by -1 \edef\lastk{\the\count50}%
    \foreach \k in {0,...,\lastk}{%
      \ExtractDigit{\B}{\k}{\dval}%
      \ifnum\dval=0
        \edef\lenk{1}% one “0” box
      \else
        \edef\PP{\number\numexpr \A*\dval\relax}%
        \NumberLen{\PP}{\lenk}%
      \fi
      % top edge of this row: just under the rule, then step down per row
      \pgfmathsetmacro{\rowY}{\ruleY - \gap - (\k)*(1.0+\rowskip)}
      \pgfmathtruncatemacro{\rightx}{\slen - \k}
      \PlaceBoxes{\lenk}{\rightx}{\rowY}
    }

    % Sum rule and final answer (width = len(A*B)), tightly aligned
  \ifnum\blen>1\relax
    \pgfmathsetmacro{\sumY}{\ruleY - \gap - (\blen)*(1.0+\rowskip) - \sumbuffer}
    \draw[thick] (0,\sumY) -- (\slen,\sumY);
    \pgfmathsetmacro{\ansY}{\sumY - \gap}
    \PlaceBoxes{\slen}{\slen}{\ansY}
  \fi
  \end{tikzpicture}
  \end{center}
  \end{minipage}
}

% ============================= Document =============================
\begin{document}

%\Large\textbf{Multiplication Practice - Expanded Format}

\vspace{0.4cm}
\multproblem{23}{14}
\hfill
\multproblem{31}{22}

\vspace{1.7cm}
\multproblem{42}{13}
\hfill
\multproblem{123}{21}

\vspace{1.7cm}
\multproblem{142}{13}
\hfill
\multproblem{215}{321}

\newpage

\vspace{0.5cm}

\multproblem{234}{6} % 3×1 included here
\hfill
\multproblem{8}{567}

\vspace{3cm}

\end{document}