条件语句不起作用，我收到一条错误消息“缺失数字被视为零”
\documentclass[border=10pt,tikz]{standalone}
\usepackage{xcolor}
\definecolor{lava}{rgb}{0.81, 0.06, 0.13}
\definecolor{myblue}{rgb}{0.0, 0.30, 0.60}
\usepackage {ifthen}
\usepackage {tikz}
\usetikzlibrary{calc}
\definecolor{metallicBlue}{RGB}{44,88,128}
\tikzstyle arrowstyle=[scale=1]
\usetikzlibrary{arrows,shapes,positioning}
\usetikzlibrary{angles, arrows.meta,quotes}
\usepackage{pgfplots,tikz}
\usetikzlibrary{angles, arrows.meta,quotes}
\usepackage{pgfplots,tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\def\t{1}
\foreach \angle in {0,0.5,...,11}
{
\begin{tikzpicture}[dot/.style = {circle, fill, minimum size=4pt,inner sep=0pt},arr/.style = {thick,cap=round, -{Straight Barb[angle=45:4pt 3]}}]
\pgfmathtruncatemacro{\ang}{\angle+1};
\pgfmathtruncatemacro{\angg}{\angle+2};
\ifnum\value{\angle} <12{
\fill[metallicBlue] (0,0) rectangle (10.5,\t);
\fill[myblue!20!white] (0,\t) rectangle (10.5,4.25);
\draw plot[samples at={0,.5,...,\angle}] (\x,{2.625+1.6*sin(deg(\x*pi))});
\draw[dashed] plot[samples at={0,1,...,\ang}] (\x,{2.625+1.6*sin(deg(\x*pi/2))});
\draw[lava] (0,2.625)--(\angg,2.625);
\fill[metallicBlue] (0,4.25) rectangle (10.5,4.25+\t);
\node(d)[]at(11.5,0){};
\node[] at(5.5,0.5){$n_2$};
\node[] at(5.5,2.5){$n_1$};}
else
{ \node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi))}){};
\node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi/2))}){};
\node (n3) [dot, color=myblue] at(\angg,2.625){};}
\fi
\end{tikzpicture}}
\end{document}
答案1
ifnum仅用于整数，对于浮点数ifdim也可以使用。
\documentclass[border=10pt,tikz]{standalone}
\usepackage{xcolor}
\definecolor{lava}{rgb}{0.81, 0.06, 0.13}
\definecolor{myblue}{rgb}{0.0, 0.30, 0.60}
\usepackage {ifthen}
\usepackage {tikz}
\usetikzlibrary{calc}
\definecolor{metallicBlue}{RGB}{44,88,128}
\tikzstyle arrowstyle=[scale=1]
\usetikzlibrary{arrows,shapes,positioning}
\usetikzlibrary{angles, arrows.meta,quotes}
\usepackage{pgfplots,tikz}
\usetikzlibrary{angles, arrows.meta,quotes}
\usepackage{pgfplots,tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\def\t{1}
\foreach \angle in {0,0.5,...,11}
{
\begin{tikzpicture}[dot/.style = {circle, fill, minimum size=4pt,inner sep=0pt},arr/.style = {thick,cap=round, -{Straight Barb[angle=45:4pt 3]}}]
\pgfmathtruncatemacro{\ang}{\angle+1};
\pgfmathtruncatemacro{\angg}{\angle+2};
\ifdim\angle pt <12.0pt{
\fill[metallicBlue] (0,0) rectangle (10.5,\t);
\fill[myblue!20!white] (0,\t) rectangle (10.5,4.25);
\draw plot[samples at={0,.5,...,\angle}] (\x,{2.625+1.6*sin(deg(\x*pi))});
\draw[dashed] plot[samples at={0,1,...,\ang}] (\x,{2.625+1.6*sin(deg(\x*pi/2))});
\draw[lava] (0,2.625)--(\angg,2.625);
\fill[metallicBlue] (0,4.25) rectangle (10.5,4.25+\t);
\node(d)[]at(11.5,0){};
\node[] at(5.5,0.5){$n_2$};
\node[] at(5.5,2.5){$n_1$};}
else
{ \node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi))}){};
\node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi/2))}){};
\node (n3) [dot, color=myblue] at(\angg,2.625){};}
\fi
\end{tikzpicture}}
\end{document}
答案2
该命令\value仅当其参数是 LaTeX 计数器的名称时才有用；因此\value{\angle}肯定是错误的。
此外，\ifnum只能比较整数，不能比较浮点数。
你可以使用解决方法（可能有更好的方法）
\pgfmathparse{ifthenelse(\angle<12,1,0)}
\ifodd\pgfmathresult\relax
<true text>
\else
<false text>
\fi
注意真文与假文之间不要加括号。
由于\pgfmathresult当测试返回真时产生 1，否则产生 0，因此条件\ifodd将选择所需的分支。
不过，我不确定你为什么要测试\angle小于 12。
提示：不要\def在外层使用；\foreach可以在代码内部使用，因为每次循环结束时都会恢复以前的含义。
完整代码：
\documentclass[border=10pt,tikz]{standalone}
\usepackage{xcolor}
\usepackage{ifthen}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{calc}
\usetikzlibrary{arrows,shapes,positioning}
\usetikzlibrary{angles, arrows.meta,quotes}
\usetikzlibrary{decorations.markings}
\definecolor{lava}{rgb}{0.81, 0.06, 0.13}
\definecolor{myblue}{rgb}{0.0, 0.30, 0.60}
\definecolor{metallicBlue}{RGB}{44,88,128}
\tikzset{
arrowstyle/.style={scale=1},
}
\begin{document}
\foreach \angle in {0,0.5,...,11}{
\def\t{1}
\begin{tikzpicture}[
dot/.style = {circle, fill, minimum size=4pt,inner sep=0pt},
arr/.style = {thick,cap=round, -{Straight Barb[angle=45:4pt 3]}}
]
\pgfmathtruncatemacro{\ang}{\angle+1};
\pgfmathtruncatemacro{\angg}{\angle+2};
\pgfmathparse{ifthenelse(\angle<12,1,0)}
\ifodd\pgfmathresult\relax
\fill[metallicBlue] (0,0) rectangle (10.5,\t);
\fill[myblue!20!white] (0,\t) rectangle (10.5,4.25);
\draw plot[samples at={0,.5,...,\angle}] (\x,{2.625+1.6*sin(deg(\x*pi))});
\draw[dashed] plot[samples at={0,1,...,\ang}] (\x,{2.625+1.6*sin(deg(\x*pi/2))});
\draw[lava] (0,2.625)--(\angg,2.625);
\fill[metallicBlue] (0,4.25) rectangle (10.5,4.25+\t);
\node(d)[]at(11.5,0){};
\node[] at(5.5,0.5){$n_2$};
\node[] at(5.5,2.5){$n_1$};
\else
\node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi))}){};
\node (n3) [dot, color=myblue] at(\angle,{2.625+1.6*sin(deg(\angle*pi/2))}){};
\node (n3) [dot, color=myblue] at(\angg,2.625){};
\fi
\end{tikzpicture}
}
\end{document}