[Tex/LaTex] ! LaTeX Error: File `12pt.cls’ not found

Question

Here's my code:

\documentclass{12pt}{article}
\usepackage{amssymb,amsmath,latexsym}
\begin{document}
\title{Assignment-1}
\date{\today}
\author{xyz}
\maketitle
\tableofcontents
\newpage
\section{ODE}
Hello
\subsection{Maths}
\subsubsection{Hello}
\section{Paragraph-2}
\subsection{stats}
$$a^2+b^2=c^2$$
\end{document} 

The error I keep getting:

Command Line: pdflatex.exe –interaction=errorstopmode –synctex=-1 "one.tex"
Startup Folder: C:\Users\xyz\Desktop

This is pdfTeX, Version 3.14159265-2.6-1.40.19 (MiKTeX 2.9.6930)
entering extended mode
(one.tex
LaTeX2e <2018-12-01>

! LaTeX Error: File `12pt.cls' not found.

Type X to quit or to proceed,
or enter new name. (Default extension: cls)

Enter file name:

I am new to this, please answer in a detailed manner.

Answer 1

The fix here should be simple. Use

\documentclass[12pt]{article}

instead of

\documentclass{12pt}{article}

Note the use of [12pt] as an optional argument to the \documentclass command, rather than your supply of {12pt} - a mandatory argument.