Error while installing package in RStudio - r

Question

I'm not able to install the IntroCompFinR package in RStudio due to this error:
> install.packages("IntroCompFinR")
Installing package into ‘C:/Users/HP/Documents/R/win-library/3.6’
(as ‘lib’ is unspecified)
Warning in install.packages :
package ‘IntroCompFinR’ is not available (for R version 3.6.1)

Answer 1

Try the R-Forge repo?
install.packages("IntroCompFinR", repos="http://R-Forge.R-project.org")
You may also have to install quadprog from another repo first.
install.packages("quadprog", repos="http://cran.rstudio.com")
install.packages("IntroCompFinR", repos="http://R-Forge.R-project.org")

Answer 2

install.packages("package_name") from devtools library works only when the package is enlisted in CRAN, and complies with your R version.
Three alternatives if it is available, but either not in CRAN or not compatible with your R version:
Install via Github: If your package is incorporated in a Github repository (most packages are), then you can use
install_github("github_UsernameOfAuthor/repository_name")
Other prominent repository holders include bitbucket and gitorious, for which
install_bitbucket("package_Author/repository_name")
and
install_gitorious("package_Author/repository_name")
apply respectively.
Install via R-Forge: If your repository is uploaded to R-Forge, you can use
install.packages("package_name", repos="http://R-Forge.R-project.org")
This is applicable in your case since there is an R-Forge repository for the IntroCompFinR library, with the install command being mentioned here as well.
Install via some other source URL/website: If your package has a repository somewhere on the internet, you can use the source-link to install the package via
install.packages("package_name", repos="URL")`.
Note: All of these commands are provided by devtools, which you seem to have, but just in case you don't, you can use these commands to install both devtools and your required package:
# Install directly from CRAN:
if(!require(devtools))install.packages("devtools")
devtools::install.packages("package_name")
# Install via Github:
if(!require(devtools))install.packages("devtools")
devtools::install_github("githubAuthor_username/package_name")
# Install via R-Forge or any other repository holding website:
if(!require(devtools))install.packages("devtools")
devtools::install.packages("package_name",repos="website-link")
Most package authors give installation commands in their package vignette or via their Github repository for the same, but you can acquire the package directly provided you know its name and link to the source repository.
You can use this post as a reference when installing R packages in the future.