LEDs effects changing with a button
I think you want to look at interrupts.  You are right, unless the button happens to be pressed when you read the state of it you won't see it as pressed.  If you foos take a long time to execute the you will miss button presses.  

What you can do is use 'interrupts'.  Certain pins can be configured to stop the main program and run a small bit of code (that can't do certain things).  For instance they can change the value of a global volatile variable.  Next time the program reads the variable it will read the new value (volatile prevents the value being cached by the processor).

With you current code, you would remove the digital read line, and the if (buttonState == HIGH) block and move those into you ISR.  This would mean every click would be counted.  If you wanted the ISR to stop the current foo and move on then you foos would need to check a flag that the ISR also set and when they see it they return.

In the ISR you can't call Serial.print() etc, it takes too long and your ISR won't work.  Keep it fast and small.

https://www.arduino.cc/en/Reference/AttachInterrupt
https://www.arduino.cc/en/Reference/DetachInterrupt