Try writing void swap(int a, int b) that swaps two numbers. Use int temp = a; a = b; b = temp;. Call from main, print the variables. They didn't swap. Why? Pass by value. The function gets copies.
You swapped copies, not originals. Copies die when function returns, originals unchanged. Parameters are copies. You can't modify caller's variables this way. This failure teaches what pass by value can't do.