Arduino if else code
Replace the line:

  if (A0 == HIGH) {


by this one:

  if (digitalRead(A0) == HIGH) {


If you plan on using the pin back as an analog input, use something like this:

  if (analogRead(A0) &gt; 512) {


The explanation is what Ignacio said: you were comparing the pin "name" A0 directly to HIGH instead of reading from the input named A0. To make it clearer, the two lines are equivalent:

if (A0 == HIGH)
if (0 == HIGH)


Get it?

There's more about what pin names to use with digitalRead() and analogRead() here: 


analogRead(0) or analogRead(A0) at EE.SE.