Writing a game, or any software in 1987 would be painstaking compared to the luxury we have today. Back then it was normal to run DOS and DOS can only do one thing at the time. You open your editor, write code, close your editor, run the compiler, run your program, test your program, exit program, re-launch editor, etc. Over time small improvements where made to this flow like a DOS Shell and even things like DESQView that allow for basic multitasking.
This is probably a better description (from a code point of view) on what you had to do as a programmer to write a game in the late 80s / early 90s: