Why are my if statements acting like the condition is always true?

Question

Here is my code. My issue is is that the keys are getting "pressed" even though there is nothing jumping any of the pins on the Arduino.

// UNO-HIDKeyboard-Library - Version: Latest 
// This program has been created by pcs3rd.
// Please do not change this line.
#include <HIDKeyboard.h>
HIDKeyboard keyboard;   // Initiate keyboard
// Pin deffanitions and variables...
int key0 = 2;   // Button 0 (Unused but optional)
int key1 = 3;   // Button 1
int key2 = 4;   // Button 2
int key3 = 5;   // Button 3
int key4 = 6;   // Button 4
int key5 = 7;   // Button 5
int key6 = 8;   // Button 6
int key7 = 9;   // Button 7
int key8 = 10;  // Button 8
int led0 = 13;  // Indicator light.
int state0 = 0; // Button 0
int state1 = 0; // Button 1
int state2 = 0; // Button 2
int state3 = 0; // Button 3
int state4 = 0; // Button 4
int state5 = 0; // Button 5
int state6 = 0; // Button 6
int state7 = 0; // Button 7
int state8 = 0; // Button 8

void setup() {
   keyboard.begin();    // Start keyboard emulation 
   Serial.begin(9600);  // Start Serial Output
   delay(300);          // Wait to be recognized be PC.
   pinMode(key1, INPUT_PULLUP); // set pin mode
   pinMode(key2, INPUT_PULLUP); // set pin mode
   pinMode(key3, INPUT_PULLUP); // set pin mode
   pinMode(key4, INPUT_PULLUP); // set pin mode
   pinMode(key5, INPUT_PULLUP); // set pin mode
   pinMode(key6, INPUT_PULLUP); // set pin mode
   pinMode(key7, INPUT_PULLUP); // set pin mode
   pinMode(key8, INPUT_PULLUP); // set pin mode
   pinMode(led0, OUTPUT);       // set pin mode
   Serial.println("Startup Completed!");
}


void loop() {
   // write state info to vars
   state0 = digitalRead(key0); // Button 0
   state1 = digitalRead(key1); // Button 1
   state2 = digitalRead(key2); // Button 2
   state3 = digitalRead(key3); // Button 3
   state4 = digitalRead(key4); // Button 4
   state5 = digitalRead(key5); // Button 5
   state6 = digitalRead(key6); // Button 6
   state7 = digitalRead(key7); // Button 7
   state8 = digitalRead(key8); // Button 8
   if (state0 == HIGH) {       // Button 0
     digitalWrite(led0, HIGH);
     // keyboard.pressSpecialKey(0x68); (You can enter a scancode instead of 0x68,)
     Serial.println("state0");
     delay(30);
   }
   if (state1 == HIGH) { // Button 1
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x68);
     Serial.println("state1");
     delay(30);
   }
   if (state2 == HIGH) { // Button 2
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x69);
     Serial.println("state2");
     delay(30);
   }
   if (state3 == HIGH) { // Button 3
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x6A);
     Serial.println("state3");
     delay(30);
   }
   if (state4 == HIGH) { // Button 4
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x6B);
     Serial.println("state4");
     delay(30);
   }
   if (state5 == HIGH) { // Button 5
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x6C);
     Serial.println("state5");
     delay(30);
   }
   if (state6 == HIGH) { // Button 6
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x6D);
     Serial.println("state6");
     delay(30);
   }
   if (state7 == HIGH) { // Button 7
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x6E);
     Serial.println("state7");
     delay(30);
   }
   if (state8 == HIGH) { // Button 8
     digitalWrite(led0, HIGH);
     keyboard.pressSpecialKey(0x0F);
     Serial.println("state8");
     delay(30);
   }
   digitalWrite(led0, LOW);
   Serial.println("scan");
   delay(30);
}

Yet, even though I have 'if' statements, the code still gets executed, as shown in my monitor:

Startup Completed!

state0
hstate1
istate2
jstate3
kstate4
lstate5
mstate6
nstate7
state8
scan
state0
hstate1
istate2
jstate3
kstate4
lstate5
mstate6
nstate7
state8
scan

Are there any hints to what could be going on? I reformatted the code for readability, but it is pretty much the same as before. Also, I am not using pin 0 or one. I am using 13 for onboard LED.

Answer 1

Microcontroller pins tend to read LOW when left floating (but not always!). However, pin 1 is used to communicate with the USB-UART converter, and I believe it is set HIGH in the idle state. So assuming you are not pressing any buttons, keys 2-8 will be in the LOW state by default, but key 1 will be HIGH. Hence when defaultCase = HIGH;, the first if is triggered. When defaultCase = LOW; all if's but the first one fire up. Solution — don't use digital pin 1 (edit: avoid pin 0 and maybe 13 as well).

Edit: The answer above refers to the original code without the pull-up resistors enabled.