IF/ELSE and Which Branch Runs

An IF/ELSE statement tests a condition that can only be true or false. If it's true, the program runs the code inside the IF branch and skips the ELSE branch completely. If it's false, the program skips the IF branch and runs the ELSE branch instead. There's no scenario where both run, and no scenario where neither runs. This is what makes it a true fork in the road rather than two separate checks.

Picture the flow of control as a single thread moving down the program. At the IF/ELSE, that thread splits into two possible paths based on the condition, but only one path actually gets walked. Once that chosen branch finishes executing, the thread rejoins the main flow right after the ELSE block, and the program continues as normal. The two branches never both execute and never execute partially; the split and rejoin happen cleanly every single time the structure runs.

This matters most when you compare IF/ELSE to two separate IF statements. With IF/ELSE, the branches are mutually exclusive by construction, since only one condition decides everything. With two back-to-back IF statements, each condition is checked independently, so both blocks could run, neither could run, or just one could, depending on how the conditions relate. That independence is exactly why IF/ELSE is the tool for either-or choices, while separate IFs suit situations where multiple things might need to happen at once. This distinction sets up later work with chained IF/ELSE IF structures for more than two outcomes.