Build is not the same thing as run. Build rebuilds the program from scratch. This means:
1. Each source file (you may have more than one) is
2. All resulting object files are linked into an executable.
T-T-t-t-t-hat's a-a-a-a-l-l-l-l f-f-f-f-olks. If you want to run it, do so.
You need to do two things: continue your studies; learn your tools. I doubt seriously that you would buy plans for a gazebo and buy a couple K worth of power tools and start in without reading both the plans AND the manuals for the tools. If you would, don't call me to donate extra fingers for you. Don't do it in programming, either. Your tool (the compiler/IDE) has help files. Use them.