Calling a function once only

hi. don't think need post whole code in nutshell have float switch providing either high or low. whenever changes low high want call pwr1on(), when goes high low want call pwr1off().

code: [select]

void pwr1on()         
{
  digitalwrite(22, high);
  pwr1=1;
  blynk.virtualwrite(v30, 1);
  blynk.virtualwrite(v40, 1);
}

void pwr1off()
{
  digitalwrite(22, low);
  pwr1=0;
  blynk.virtualwrite(v30, 0);
  blynk.virtualwrite(v40, 0);
}


void loop()
{
  sensorval1 = digitalread(50);
 
  if (sensorval1 == low)
  {
    pwr1on();
  }
  else
  {
    pwr1off();
  }
}

i can't figure out way of calling once , not repeatedly.

see ide example digital/statechangedetection.

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