我不确定为什么我会收到 hbox 错误。
\documentclass{exam}
\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing}
\usetikzlibrary{shapes,calc}
\tikzset{fontscale/.style={font=\relsize{#1}}}
\tikzstyle{startstop} = [ellipse, minimum width=3cm, minimum height=1cm, line width=0.0625cm,
text centered, text width = 5em, draw=black, fill=red!30]
\tikzstyle{process} = [rectangle, rounded corners, minimum width=1.9cm, minimum height=1cm, line width=0.0625cm, text centered, text width = 5em, text width=3cm, draw=black, fill=orange!30]
\tikzstyle{decision} = [diamond, minimum width=1.5cm, minimum height=0.5cm, text centered, text width = 5em, line width=0.03125cm, draw=black, fill=green!30]
\tikzstyle{elbow} = [ellipse, minimum size=10pt, draw=black, fill=black]
\tikzstyle{arrow1} = [line width=0.0625cm,->,>=stealth]
\tikzstyle{arrow2} = [line width=0.0625cm,-]
\begin{document}
\begin{center}
\begin{tikzpicture}[node distance=2cm]
\node (start) [startstop] {Understand Problem};
\node (pro1) [process, below of=start, yshift=-1.5cm] {Make a Plan};
\node (pro2) [process, right of=pro1, xshift=2.9cm] {Solve the Problem};
\node (dec1) [decision, above of=pro2, yshift=1.5cm] {Validate Results};
\node (end) [startstop, right of=dec1, xshift=2.9cm] {Report Conclusion};
\draw [arrow1] (start) -- (pro1);
\draw [arrow1] (pro1) -- (pro2);
\draw [arrow1] (pro2) -- (dec1);
\draw [arrow1] (dec1) -- node [shift=(90:0.5)] {N} (start);
\draw [arrow1] (dec1) -- node [shift=(90:0.5)] {Y} (end);
\end{tikzpicture}
\end{center}
\end{document}