Use Text Input Instead of Interactive Console
When you run your code (F9), on the bottom of the page, there is a panel for
- command line arguments
- standard input
Standard input can be changed from "interactive console" to Text, where you can just copy paste your text file and use it as input for your program. (It will appear in argv of main()).
Upload Your File
You can upload files to your project. Use the button on the left of the "RUN" button. After this, you can just open your file as you'd do it normally (e.g. FILE * myFile = fopen("myfile.txt", "r");