GNU/Linux Ubuntu 20.04 Installing GCC 10.3 – QuickStart Guide
Hi! The Tutorial shows you Step-by-step How to Install the GNU Compiler Collection 10.3.x in Ubuntu 20.04 Focal LTS GNU/Linux.
And the GCC 10.3 for Ubuntu 20.04 is a Compilers Collection currently supporting C, C++, Objective-C, Objective-C++, Fortran, Ada, D, Go, and BRIG (HSAIL) Languages.
The GCC 10.3 back-ported 178 Bug Fixes to the release compared to GCC 10.2.
Especially relevant: now the GCC 10.3 is available on the default Apt Updates Repository.
Finally, you may be interested instead about How to Install Latest GCC 11.2 from Source on Ubuntu.

1. Terminal Getting-Started Guide
How to QuickStart with Command Line on Ubuntu GNU/Linux:
First Update the Apt Repo Sources with:
sudo apt update
Authenticate with the User Admin Pass.
If Got “User is Not in Sudoers file” then see: How to Enable sudo.
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