Apple actively discourages most attempts to make the iPad more programmer friendly so while the hardware is perfectly capable, the software that runs on it is not meant for developers.

If you are Ok with a Terminal only workflow and you only care about C programming as in learning just the language, you should be able to do it.

Install iSH from the App Store. With iSH installed you can use the apk package manager to install VIM and GCC. You should be able for example to follow a basic book intro to C. iSH, while based on 32 bits Alpine Linux, it is not a complete operating system, so if you care about low level Linux programming you will be better off with a second hand laptop with Debian or Ubuntu on it.

Even a Chromebook with Linux enabled will run circles around your iPad from a programming point of view.