FRDM-KL25Z programming using InterruptIn
My answer is based on your comment in the question. 
Since your main aim is to detect if a switch is pressed or not, a sample algorithm would look like:

ISR:

wait for pin to go low(depends on switch)
 if low,increment a variable
 else,clear the variable

If variable is greater than debounce time for switch(70ms maybe for switches)
 Set,Switch pressed flag


Main:

while(1)
{
 if Switch is pressed
  do something(may be increment "selection" here)
}


If your interrupt is configured to trigger every 1ms,the Switch pressed flag will set when atleast 70 consecutive low values are read at the pin.
Detecting if a pin is pressed or not using an interrupt everytime the value at the pin changes may not be a good idea due to noise.Use a timer interrupt instead.

For details regarding the syntax of your code,I suggest StackOverflow.