logic for arduino programming?

Projects General Guidance
1

i have two different programs of arduino which i want to merge as a single program with some logic like if a particular button is on jump to program 1 or if button is off jump to program 2 but that would be a waste of energy as button will be on or whole time program 1 is running. Is there more efficient way to do the switching. note for demonstration the arduino will be battery powered and not connected to laptop or pc.

2

Could be at the beginning of your loop, digitalRead for a switch and you'd go to one function or another from there.
Even then, from either function you could check that switch to go to the other function.

3 
const byte buttonPin = 3;

void loop() {
   if (digitalRead(buttonPin)) {
      loop1();
    }
    else {
        loop2();
    }
}