Use keypad to replace the keyboard

I'm using the arduino's 4x4 keypad to replace the keyboard on my Laptop, but I don't know where should I insert the code, should I insert in loop or send? and can I hold the password until I pressed # then send?

// TX

#include <SPI.h>
#include <nRF24L01.h>
#include <RF24.h>
#include <Key.h>
#include <Keypad.h>

#define CE_PIN   7
#define CSN_PIN  8

const byte slaveAddress[5] = {'R','x','A','A','A'}; //slaveaddress
const byte masterAddress[5] = {'T','X','a','a','a'}; //masteraddress


RF24 radio(CE_PIN, CSN_PIN); // Create a Radio

const byte ROWS=4;
const byte COLS=4;
char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowPins[ROWS]={5,4,3,2};
byte colPins[COLS]={14,15,16,17};
char dataReceived[15]; // to hold the data from the slave - must match replyData[] in the slave
bool newData = false;
char customKey=0;
unsigned long currentMillis;
unsigned long prevMillis;
unsigned long txIntervalMillis = 500; // 每半秒讀取一次
char cmd[15];
char password[4];
char test[2]={'O','K'};
Keypad customKeypad = Keypad(makeKeymap(keys),rowPins,colPins,ROWS,COLS);
char customKey;
char a[5];
//============

void setup() {

    Serial.begin(115200);
   
    Serial.println("MasterSwapRoles Starting");

    radio.begin();
    radio.setDataRate( RF24_250KBPS ); 

    radio.openWritingPipe(slaveAddress);
    radio.openReadingPipe(1, masterAddress);

    radio.setRetries(3,5); // delay, count
    send(); // to get things started
    prevMillis = millis(); // set clock
}

//=============

void loop() {
    
    currentMillis = millis();
    if (currentMillis - prevMillis >= txIntervalMillis) {
        send();
        prevMillis = millis();
    }
    getData();
    showData();
    showDatafailed();
}

//====================

void send() {
      
              radio.stopListening();
              bool rslt;
              
                if(Serial.available())
                {
                    Serial.readBytes(cmd,100);
                    Serial.println(atol(cmd));
                    rslt = radio.write( &cmd, sizeof(cmd) );
                    radio.startListening();
                    Serial.println("Data Sent");
                    if (rslt) {
                        Serial.println("Received...OK");
                    }
                    else {
                        Serial.println("Received...failed");
                    }
                }
              
            
}

//================

void getData() {

int a=6;
int i=0;
int j=0;
    if ( radio.available() ) {
        radio.read( &dataReceived, sizeof(dataReceived) );
        newData = true;
        for(i=0;i<a;i++)
        {
          if(dataReceived[i] == test[i])
            {
              showData();
            }
            else
            {
              showDatafailed();
              
            }
            
            
              
            
          }
        }
        
}

//================

void showData() {
    if (newData == true) {
        Serial.print("Data received...");
        Serial.print(dataReceived);
        Serial.println("\n");
        newData = false;
    }
}

//================
void showDatafailed() {
    if (newData == true) {
        Serial.print("Data received...");
        Serial.print(dataReceived);
        Serial.println("\n");
        newData = false;
    }
}
// RX

#include <SPI.h>
#include <nRF24L01.h>
#include <RF24.h>


#define CE_PIN   7
#define CSN_PIN  8

const byte slaveAddress[5] = {'R','x','A','A','A'};
const byte masterAddress[5] = {'T','X','a','a','a'};
char pass[4]={'7','4','1','4'};
RF24 radio(CE_PIN, CSN_PIN); // Create a Radio

char dataReceived[15]; // must match dataToSend in master
char replyData[2]= {'O','K'}; // the two values to be sent to the master
char replyDatafalse[6]={'f','a','i','l','e','d'};
int newData = 0;

unsigned long currentMillis;
unsigned long prevMillis;
unsigned long txIntervalMillis = 500; // 每半秒讀取一次


void setup() {

    Serial.begin(115200);

    Serial.println("SlaveSwapRoles Starting");

    radio.begin();
    radio.setDataRate( RF24_250KBPS );

    radio.openWritingPipe(masterAddress); // NB these are swapped compared to the master
    radio.openReadingPipe(1, slaveAddress);

    radio.setRetries(3,5); // delay, count
    radio.startListening();

}

//====================

void loop() {
    getData();
    showData();
    send();
}

//====================

void send() {
    if (newData == 1) {
        radio.stopListening();
            bool rslt;
            rslt = radio.write( &replyData, sizeof(replyData) );
        radio.startListening();

        Serial.print("Reply Sent: ");
        Serial.print("OK \n");
        

        if (rslt) {
            Serial.println("Received...OK\n");
        }
        else {
            Serial.println("Received...failed\n");
        }
        Serial.println();
        newData = 0;
    }
    else if(newData==2)
    {
      radio.stopListening();
            bool rslt;
            rslt = radio.write( &replyDatafalse, sizeof(replyDatafalse) );
        radio.startListening();

        Serial.print("Reply Sent: ");
        Serial.print("failed \n");

        if (rslt) {
            Serial.println("Received...OK\n");
            
        }
        else {
            Serial.println("Received...failed\n");
        }
        Serial.println();
        newData=0;
    }
}

//================

void getData() {
int a=4;
int i=0;
int j=0;
int k=0,z=0;
    if ( radio.available() ) {
        radio.read( &dataReceived, sizeof(dataReceived) );
        for(i=0;i<a;i++)
        {
          if(dataReceived[i]== pass[i])
            {
              k++;
            }
            else
            {
              z++;
            }
          }
          if(k==a)
          {
            newData=1;
          }
          else
          {
            newData=2;
          }
    }
   }
        
    

//================

void showData() {
    if (newData == 1) {
        Serial.print("Data received...OK\n");
    }
    else if(newData == 2)
    {
      Serial.print("Data received...OK\n");
    }
}

//================

You appear to be using a radio. Are you making a wireless keyboard?

Nope, I'm using nrf24 to send password between two chips, the keyboard is just used to input the password

It looks like all you have now is a sketch that sends data from the TX sketch on one Arduino to the RX sketch on the other.

The TX sketch defines a Keypad but doesn't seem to be using it at all. You should look at the examples from the Keypad library to see how you would read characters from the keypad.

The RX sketch is probably where you would want the Arduino to act as a USB keyboard. To do that you need the Keyboard library and an Arduino with native USB, like the Leonardo or the Micro. The Keyboard library doesn't work on an UNO, Nano, Mini, or Mega. Again, the library examples are a good way to learn how to use the library.