Wrong spacing when inserting text with command

Question

I defined a new command called \dofile to reference a file that does not have a permanent name yet. The command by default returns the name of the file in typewriter font, since that is how I want it to appear in most places in the document. But since I wanted to have access to the file name without formatting just in case, I added an optional parameter that, when set equal to 1, returns the file name in plain text.

I am having trouble getting the spacing to be correct in all four possible use-cases.

In the provided working example, the spacing is correct in all but the second line, in which I call the command without the optional argument, outside of the \texttt{} environment. I was able to fix the spacing, but at the cost of adding extra space to the fourth case (fifth line), in which I call the command without the optional argument, inside of the \texttt{} environment.

My code is the following:

\documentclass{article}
\setlength\parindent{0pt}
\newcommand{\dofile}[1][0]{%
    \ifnum#1=1
    \texttt{MyFile.do}%
    \else%
    MyFile.do%
    \fi}
\begin{document}
    In this line I reference MyFile.do without the command.\\
    In this line I reference \dofile without the optional argument.\\
    In this line I reference \texttt{MyFile.do} without the command.\\
    In this line I reference \dofile[1] with the optional argument.\\
    In this line I reference \texttt{\dofile} without the optional argument.
\end{document}