digitalRead problem

Projects General Guidance
1

hi guys
i'm using arduino mega
i'm trying to turn on a led (on pin 30) when pin 31 goes HIGH
but the problem is when I put a jumper on pin 31 (jumper isn't connected to anything in the other side) led start blinking
and stop after a while but when i move my hand close to the jumper the led start blinking again
so please help me
that's my code:

int Switch = A7;
 int flag;

void setup() {
 Serial.begin(9600);
  pinMode(Switch, INPUT);
  pinMode(30,OUTPUT);
   
}

void loop() {
  // put your main code here, to run repeatedly:

          if(digitalRead(Switch)==HIGH){
            flag =1;
            digitalWrite(30, HIGH);
            if(digitalRead(30)==HIGH){
  Serial.print("b");
          }}
           if(digitalRead(Switch)==LOW){
            flag =0;
            digitalWrite(30, LOW);
              if(digitalRead(30)==LOW){
  Serial.print("f");
          }}
}
2

Your input is floating and the wire picks up noise.

Add a pull-up (or use
* *pinMode(Switch, INPUT_PULLUP);* *
) and wire the switch between pin and ground. Note that a pressed switch now results in LIW.

Or use a pull-down resistor and wire the switch between pin and Vcc