Arduino button and lcd for monitoring data

hi everyone i am making solar charger circuit in this site Solar Panel Battery Charge Controller Using Arduino in the code solar data is printed to serial but i need to change that with three button to show in lcd
for example if i press button1 it will display the Vin and if i press the button2 it will show the Vbat how can i modify the code to accomplish this , i am open to all suggestions if anyone can help me i would be very apreciated.

Best Regards…

/*
  This also has the ability to monitor system
 settings through the serial port.
*/

#define Vin 0 // AD0
#define Vbat 1 // AD1

#define Ioutput 2 // AD2 read ACS712 current

#define LED1 12 // red low Vin
#define LED2 10 // green charged
#define  ChargeON 11 // charge current on
#define POWenable 3


// for use with PWM DP3
#define FULL 255
#define HALF 128
#define QUARTER 64
#define OFF 0

int x;
int y;

// these two variables can be changes
// for differing on/off times.
int chon = 5000; // charge on time
int choff = 2000; // charge off time

int CP = 310; // charge point variable
// CP sets the battery charge voltage level. Can vary from 300-340.
void setup()   {

  pinMode(LED1, OUTPUT); 
  pinMode(LED2, OUTPUT);  
  pinMode(ChargeON, OUTPUT);
  pinMode(POWenable, OUTPUT);

  digitalWrite(LED1, HIGH);
  digitalWrite(LED2, HIGH);
  digitalWrite(ChargeON, HIGH);
  digitalWrite(POWenable, LOW);

  Serial.begin(9600);

  delay(500);

}

void loop()   {

  Serial.print("CP = ");
  Serial.println(CP);


  x = analogRead(Vin); 
  // voltage from solar panel
  //under CP on ADC indicates not 
  // enough voltage to charge battery
  // ~ 0.041 is derived from reading the 
  // voltage with a DVM
  // the dividing by the returned 
  // int value.
  Serial.print(x);
  Serial.print("   ");
  Serial.print("Vin = ");
  Serial.println(x * .041); 



  y = analogRead(Vbat); 
  // voltage on battery to be charged
  // over or equal to CP on ADC indicates 
  // fully charged battery
  Serial.print(y);
  Serial.print("   ");
  Serial.print("Vbat = ");
  Serial.println(y * .041);

  // red LED
  if (x < CP) digitalWrite(LED1, LOW);
  else digitalWrite(LED1, HIGH);
  // LED on indicates low or no input voltage

  // green LED
  if (y > CP) digitalWrite(LED2, LOW); 
  else if (y <= CP) digitalWrite(LED2, HIGH); 
  // LED on means battery is charged


  if ((x > y) && (y <= CP) && (x > CP))  { 
    // check input voltage and voltage on battery
    // turn on charge cycle if voltage input 
    // good AND battery voltage low.


    if (y <= CP)   { // turn on voltage to battery
      // uncomment below will shorton ON time as charge
      // nears completion. 
      // chon = (CP - y) * 100;
      

      // turn on charge LED
      digitalWrite(ChargeON, LOW);

      // charge switching transistor 
      // can be pulse-width modulated
      // four values are OFF, QUARTER, HALF, FULL
      // This uses DP3.
      analogWrite(POWenable, FULL);

      // print chon value
      Serial.print("chon = ");
      Serial.print(chon);
      Serial.print("   ");

      delay(2000);

      // this section read a Hall effect current sensor
      // if attached. It read about 510 with no current flow
      // 1 amp causes a change of 40 or .2v as measured
      // with a DVM. Thus .2 / 40 = .025
      // This can be used to display charge current.
      // float temp = (analogRead(Ioutput) - 510) * .025;
      // This could tested for heavy charge current from 
      // a nearly dead battery which can be limited to
      // a safe value by cutting the duty cycle back
      // POWenable to QUARTER or HALF.
      int temp = analogRead(Ioutput);
      Serial.print(temp); 
      Serial.print("    I out = ");
      Serial.print((temp - 506) * .0283);
      Serial.println(" amps. ");



      delay(chon); // ON wait 
      digitalWrite(ChargeON, HIGH); // Charge LED off
      analogWrite(POWenable, OFF);  // turn off MOSFET
    }



  } // end if

  // turn off charge enable
  delay(choff); // OFF wait
}

Very similar problem here
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