Verify the PATH:

Open a new Command Prompt window and type the following command to verify if Rtools is in the PATH:

gcc --version This should display the GCC version information if Rtools is correctly added to the PATH. If it seems that gcc is still not recognized, which indicates that Rtools might not be properly installed or added to your system PATH. Let's make sure we get it right this time.

Detailed Steps to Fix the Issue: Reinstall Rtools:

First, uninstall any previous versions of Rtools from your system.

Download and install Rtools from Rtools. Make sure to follow the installation instructions carefully.

Verify Installation Directory:

By default, Rtools 4.0 and later should be installed in C:\rtools40.

Add Rtools to the PATH:

Right-click on the Start button and select System.

Click on Advanced system settings on the left side.

In the System Properties window, click on the Environment Variables button.

In the Environment Variables window, find and select the Path variable under System variables and click on Edit.

In the Edit Environment Variable window, click on New and add the following paths:

C:\rtools40\usr\bin C:\rtools40\mingw64\bin Save Changes:

Click OK to close all the windows.

Verify the PATH:

Open a new Command Prompt window and type the following command to verify if Rtools is in the PATH:

gcc --version This should display the GCC version information if Rtools is correctly added to the PATH.

Restart RStudio:

Close and reopen RStudio to ensure it recognizes the updated PATH.

Reinstall xfun and knitr:

Run the following commands in R to install the required packages:

R install.packages("xfun", type = "source") install.packages("knitr", type = "source")

Finally, load the knitr library to confirm that it has been installed successfully:

R library(knitr) Following these detailed steps should resolve the issue.