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There's a 100Ω resistor we use to connect the input pin to either HIGH or LOW voltage. Why is it there? Well, lets say you accidentally set P2 to be an OUTPUT type pin, but then you connected it to 5V. If you write a LOW to the pin (0V) but its connected to HIGH (5V), you've basically caused a short circuit at that pin. This isn't very good for the pin and could damage it! The 100Ω resistor acts as a buffer, to protect the pin from short circuits.

Why is it there? Well, lets say you accidentally set P2 to be an OUTPUT type pin, but then you connected it to 5V. If you write a LOW to the pin (0V) but its connected to HIGH (5V), you've basically caused a short circuit at that pin.

jesse skrev:Men du gör inte fel. Om du en gång satt dessa pinnar som ingångar så behöver du ju aldrig ändra på det någonsin. Skit i motståndet, det är helt onödigt, om du vet vad du gör.

Nu vet jag inte vad du tänkt göra, men du ska alltså ha ingångar på en Arduino kopplad till knapparna? Det finns ju fortfarande inget hinder att ha 100-1000-ohm motstånd till ingången, det påverkar ju i så fall varken knappar eller LED eller signalen till gamepaden.

There are also convenient 20K pullup resistors built into the Atmega chip that can be accessed from software. These built-in pullup resistors are accessed in the following manner.
pinMode(pin, INPUT); // set pin to input
digitalWrite(pin, HIGH); // turn on pullup resistors

Note that the pullup resistors provide enough current to dimly light an LED connected to a pin that has been configured as an input. If LED's in a project seem to be working, but very dimly, this is likely what is going on, and the programmer has forgotten to use pinMode() to set the pins to outputs.
Note also that the pullup resistors are controlled by the same registers (internal chip memory locations) that control whether a pin is HIGH or LOW. Consequently a pin that is configured to have pullup resistors turned on when the pin is an INPUT, will have the pin configured as HIGH if the pin is then swtiched to an OUTPUT with pinMode(). This works in the other direction as well, and an output pin that is left in a HIGH state will have the pullup resistors set if switched to an input with pinMode().

//int   inputN[3] = {inputType, pinNo, dataResolution}

int  input1[3] = {'d', 23, 1}; 
int  input2[3] = {'d', 25, 1}; 
int  input3[3] = {'d', 27, 1}; 
int  input4[3] = {'d', 29, 1}; 
int  input5[3] = {'d', 31, 1}; 
int  input6[3] = {'d', 33, 1}; 
int  input7[3] = {'d', 35, 1}; 
int  input8[3] = {'d', 37, 1}; 
int  input9[3] = {'d', 39, 1}; 
int  input10[3] = {'d', 41, 1}; 
int  input11[3] = {'d', 43, 1}; 
int  input12[3] = {'d', 45, 1}; 
int  input13[3] = {'d', 47, 1}; 
int  input14[3] = {'d', 49, 1}; 
int  input15[3] = {'d', 51, 1}; 
int  input16[3] = {'d', 53, 1};

#define kUsedInputs  16       // the 'numUsedInputs' first inputs in the list are currently used
    
// IMPORTANT: always first define the digital inputs, then the analog ones!
int* inputs[kUsedInputs] = {input1,input2,input3,input4,input5,input6,input7,input8,input9,input10,input11,input12,input13,input14,input15,input16,};
                       
unsigned short switches[4] = {0,0,0,0};          // memory space for up to 64 switches

int numUsedInputs = kUsedInputs;                                                
int numUsedAnalogInputs = 0;                    // the 'o' inputs are also listed as analog inputs....
int numUsedDigitalInputs = 16;
int numDataBytes;