$string .= " world."; # Concatenate and assign. Same as... $string = $string . " world."; $num += 5; # Add and assign. Same as... $num = $num + 5; $num -= 5; # Subtract and assign. Same as... $num = $num - 5; $num *= 5; # Multiply and assign. Same as... $num = $num * 5; $num /= 5; # Divide and assign. Same as... $num = $num / 5;