trouble of installing the package

[xpcui]

I tried to use the following two commends to install the packages "harmony" and "scPred", but getting the error message about c++ compiler. I have R 4.0.3
devtools::install_github("immunogenomics/harmony")
devtools::install_github("powellgenomicslab/scPred")

/Library/Frameworks/R.framework/Versions/4.0/Resources/library/RcppArmadillo/include/armadillo_bits/compiler_check.hpp:50:4: error: "*** C++11 compiler required; enable C++11 mode in your compiler, or use an earlier version of Armadillo"
#error "*** C++11 compiler required; enable C++11 mode in your compiler, or use an earlier version of Armadillo"