Information needed on execution time which arduino takes?

Actually for a project I am using Arduino Mega 2560, in which I am checking about 9 if conditions which just checks numbers high or less (no complicated algorithm inside if condition) for about 90 seconds without any kind of delay or delaymicroseconds, and I am in need of checking all conditions simultaneously and I am doing it using millis function, It just gives me a random behaviour like sometimes it is ok, and sometimes it is not as fast as i Expect it to be, So, What kind of arduino board do you suggest and what time does it take to check these 9 if conditions which checks just whether the given integer is high or low ?

So it looks like you are doing something wrong with your code.
My guess is that it is line 23. However my crystal ball is on the blink at the moment so just to be safe:-
Advice

In case you didn't understand @Grumpy_Mike, post your code. Without that we are blind to your problem.

...R

... in which I am checking about 9 if conditions ...

Sounds complex. Much worse than checking 7 conditions.

How to use this forum

int led[12] = {2,3,4,5,6,7,8,9,10,11,12,13}; //declaring pins for 12 LEDS
int pb[12] = {22,23,24,25,26,27,28,29,30,31,32,33}; // declaring pins for 12 ir
int coinboxsensor1  = 34;  // push button for starting the program
int coinboxsensor2 = 35;
int lcdons = 36;
int increment = 37;
int decrement = 38;
int reset = 39;

unsigned long gameLength=90000;//games last 30 seconds
unsigned long timePerLed=3000;// allow 2 seconds per light
unsigned int maxPointsPerLed=100;
boolean playing=false;
unsigned long gameStart;
unsigned long ledStart[3];
int currentLed[3];
unsigned long score;
unsigned long timerscore;
int i;
unsigned long timerscore1= 40;

void setup()
{
  for(int n=0;n<12;n++)
    {
      pinMode(led[n], OUTPUT);
     pinMode(pb[n], INPUT);
    }
    pinMode(coinboxsensor1, INPUT);// two sensors for switching the system on 
    pinMode(coinboxsensor2, INPUT);
    pinMode(lcdons, OUTPUT);//  switching the seven segment display for score
    pinMode(increment, OUTPUT);//  incrementing the seven segment display by one
    pinMode(decrement, OUTPUT);//  decrementing the seven segment display
    pinMode(reset, OUTPUT);//  resetting the display
    
    Serial.begin(9600);
    Serial.print("Press start button to start!");

}

void loop()
{
unsigned long t=millis();

//if not playing start a new game when startButton is pressed
 if(playing == false)
  {
    int a= digitalRead(coinboxsensor1);
    int b = digitalRead(coinboxsensor2);
    
    if (a == 1 && b == 1)
    {
     playing=true;
     //wait for button to be released
     digitalWrite(lcdons, HIGH);
     delay(1000);
     digitalWrite(reset, HIGH);
     delay(1000);
     digitalWrite(reset, LOW);
     gameStart=t;
     score=0;
     startlight();
     }
     }
//only continue on if we're in the midst of a game

//Check for end of game
if ( (t-gameStart) >= gameLength) 

   {
     endGame();
     return;
   }

//Check for timeout on current led
for(i = 0; i<3; i++)
{
  if( (t - ledStart[i]) > timePerLed)
  {
    nextLight();
   return;
  }
}

for(i = 0; i<3; i++)
{
  if (digitalRead(pb[currentLed[i]]) == HIGH ) // check for appropriate ir sensor for the pressed led();
  {
    digitalWrite(increment, HIGH); // incrementing the score board
    timerscore = millis();
    
    //evaluate value of this hit based on time taken

  nextLight(); 
  //Serial.print("BANG + ");
  //Serial.print (LEDvalue);
  //Serial.println(" points");
  }
}

if((t-timerscore>=timerscore1))
{
  digitalWrite(increment, LOW);
}


}

void nextLight()
{
  
//extinguish current LED  
digitalWrite (led[currentLed[i]], LOW);
//pick another
currentLed[i]=random(12);
//and light it.
digitalWrite(led[currentLed[i]], HIGH);
ledStart[i]=millis();  

}


void endGame()
{
  for(int n=0;n<12;n++)
    {
      pinMode(led[n], LOW);
    }
    for(int l = 0; l<3; l++)
    {
      digitalWrite(lcdons, HIGH);
      delay(1000);
      digitalWrite(lcdons, LOW);
      delay(1000);
    }
    

playing=false;
}

void startlight()
{
  i = 0;
  while(i<3)
  {
    currentLed[i] = random(12);
    digitalWrite(led[currentLed[i]], HIGH);
    ledStart[i] = millis();
    i++;
  }
}

I can't relate your original question to your code. Can you provide an explanation (a talk-through) of how the code is intended to work.

...R

I think you need to post a schematic as well. It sounds like you have floating inputs.

int coinboxsensor1  = 34;  // push button for starting the program

That was my guess, based on the name of the variable. NOT!

Stupid names just don't cut it.

The code looked OK except for use of pinMode() in place of digitalWrite() in endGame(). Here is the code with some clean-up done:

const int NumLEDs = 12;
const int OnLEDs = 3;

const int led[NumLEDs] = {
  2,3,4,5,6,7,8,9,10,11,12,13}; //declaring pins for 12 LEDS
const int pb[NumLEDs] = {
  22,23,24,25,26,27,28,29,30,31,32,33}; // declaring pins for 12 ir
const int coinboxsensor1  = 34;  // push button for starting the program
const int coinboxsensor2 = 35;
const int lcdons = 36;
const int increment = 37;
const int decrement = 38;
const int reset = 39;

const unsigned long gameLength=90000;//games last 30 seconds
const unsigned long timePerLed=3000;// allow 2 seconds per light
unsigned int maxPointsPerLed=100;
boolean playing=false;
unsigned long gameStart;
unsigned long ledStart[OnLEDs];
int currentLed[OnLEDs];
unsigned long score;
unsigned long timerscore;
// int i;  // NOT an appropriate name for a global variable
const unsigned long timerscore1= 40;

void setup()
{
  for(int n=0;n<NumLEDs;n++) {
    pinMode(led[n], OUTPUT);
    pinMode(pb[n], INPUT);
  }
  pinMode(coinboxsensor1, INPUT);// two sensors for switching the system on 
  pinMode(coinboxsensor2, INPUT);
  pinMode(lcdons, OUTPUT);//  switching the seven segment display for score
  pinMode(increment, OUTPUT);//  incrementing the seven segment display by one
  pinMode(decrement, OUTPUT);//  decrementing the seven segment display
  pinMode(reset, OUTPUT);//  resetting the display

  Serial.begin(9600);
  Serial.print("Press start button to start!");
}

void loop() {
  unsigned long t=millis();

  //if not playing start a new game when startButton is pressed
  if(playing == false) {
    int a = digitalRead(coinboxsensor1);
    int b = digitalRead(coinboxsensor2);

    if (a && b) {
      playing=true;
      //wait for button to be released
      digitalWrite(lcdons, HIGH);
      delay(1000);
      digitalWrite(reset, HIGH);
      delay(1000);
      digitalWrite(reset, LOW);
      gameStart=t;
      score=0;
      startlight();
    }
  }
  //only continue on if we're in the midst of a game

  //Check for end of game
  if (t-gameStart >= gameLength) {
    endGame();
    return;
  }

  //Check for timeout on current leds
  for(int i = 0; i<OnLEDs; i++) {
    if( (t - ledStart[i]) > timePerLed) {
      nextLight(i);
      return; // ??? Don't care about other LEDs?
    }
  }

  for(int i = 0; i<OnLEDs; i++) {
    // check for appropriate ir sensor for the lit led();
    if (digitalRead(pb[currentLed[i]]) == HIGH ) { 

      digitalWrite(increment, HIGH); // incrementing the score board
      timerscore = t; // Set timer for turning pulse off

      //evaluate value of this hit based on time taken

      nextLight(i); 
      //Serial.print("BANG + ");
      //Serial.print (LEDvalue);
      //Serial.println(" points");
    }
  }

  if(t-timerscore >= timerscore1) {
    digitalWrite(increment, LOW);
  }
}

void nextLight(int i) {
  //extinguish current LED  
  digitalWrite(led[currentLed[i]], LOW);
  //pick another
  currentLed[i] = random(12);
  //and light it.
  digitalWrite(led[currentLed[i]], HIGH);
  ledStart[i] = millis();  
}


void endGame() {
  // Turn off all the LEDs
  for(int n=0; n<NumLEDs; n++)
    // pinMode(led[n], LOW); // That should be digitalWrite()
    digitalWrite(led[n], LOW); 

  // Blink the score three times
  for(int l = 0; l<3; l++) {
    digitalWrite(lcdons, HIGH);
    delay(1000);
    digitalWrite(lcdons, LOW);
    delay(1000);
  }
  playing=false;
}

void startlight() {
  for (int i=0; i<OnLEDs; i++) {
    currentLed[i] = random(12);
    digitalWrite(led[currentLed[i]], HIGH);
    ledStart[i] = millis();
  }
}

@john wasser, Thanks for your reply, code started at a different shape and evolved everyday, so comments might be chaotic, anyways thanks for that cleanup let me get you the update by working on it today, Thanks, And back to the original question, how many milli seconds once, will it check for the condition if I am using Arduino Mega 2560? and if I am using Arduino Uno? I just wanted to know how to calculate it? Again, Thanks

for(int i = 0; i<OnLEDs; i++) {
    if( (t - ledStart[i]) > timePerLed) {
      nextLight(i);
      return; // ??? Don't care about other LEDs?
  }

// ??? Don't care about other LEDs?// To check the particular condition for all three glowing led's I have used "for loop" actually, To be frank i don't know any other way in which it keeps checking for the condition all the time for all three glowing led's , if you have any other way, I am glad to receive it, Please ignore any coding mistakes I am beginner at it.