both give errors like wrong assignment of const char to char* or similar errors stating incompatible data types. Can anyone tell me, what is it that I am doing wrong or show me an example of displaying the data on a oled display?? Any help is appreciated.

{
u8g2.setFont(u8g2_font_ncenB14_tr);
u8g2.firstPage();
do {
   u8g2.setCursor(0, 20);
   u8g2.print("hours"));
   } 
while ( u8g2.nextPage() );

//This is a code to display ntp time using Nodemcu

 #include <ESP8266WiFi.h>
 #include <WiFiUdp.h>
 #include <Arduino.h>
 #include <U8g2lib.h>

 #ifdef U8X8_HAVE_HW_SPI
 #include <SPI.h>
 #endif
 #ifdef U8X8_HAVE_HW_I2C
 #include <Wire.h>
 #endif

 U8G2_SH1106_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, /* reset=*/U8X8_PIN_NONE);

 char ssid[] = "123456";     //  your network SSID (name)
 char pass[] = "123456";     // your network password

//Your UTC Time Zone Differance  India +5:30
char HH = 5;
char MM = 30;

unsigned int localPort = 2390;      // local port to listen for UDP packets

* Don't hardwire the IP address or we won't get the benefits of the pool.
* Lookup the IP address for the host name instead */

//IPAddress timeServer(129, 6, 15, 28); // time.nist.gov NTP server

IPAddress timeServerIP; // time.nist.gov NTP server address

const char* ntpServerName = "time.nist.gov";

const int NTP_PACKET_SIZE = 48; // NTP time stamp is in the first 48 bytes 
of the message

byte packetBuffer[ NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing 
packets

// A UDP instance to let us send and receive packets over UDP
WiFiUDP udp;


                                  //SETUP



 void setup()
 {
 Serial.begin(115200);
 Serial.println();
 Serial.println();

 // We start by connecting to a WiFi network
 Serial.print("Connecting to ");
 Serial.println(ssid);
 WiFi.mode(WIFI_STA);
 WiFi.begin(ssid, pass);

 while (WiFi.status() != WL_CONNECTED) {
 delay(500);
 Serial.print(".");
 }
 Serial.println("");

 Serial.println("WiFi connected");
 Serial.println("IP address: ");
 Serial.println(WiFi.localIP());

 Serial.println("Starting UDP");
 udp.begin(localPort);
 Serial.print("Local port: ");
 Serial.println(udp.localPort());
 }


 //  Send an NTP request to the time server at the given address

 unsigned long sendNTPpacket(IPAddress& address)
 {
 Serial.println("sending NTP packet...");
 // set all bytes in the buffer to 0
 memset(packetBuffer, 0, NTP_PACKET_SIZE);

 // Initialize values needed to form NTP request
 // (see URL above for details on the packets)
 packetBuffer[0] = 0b11100011;   // LI, Version, Mode
 packetBuffer[1] = 0;     // Stratum, or type of clock
 packetBuffer[2] = 6;     // Polling Interval
 packetBuffer[3] = 0xEC;  // Peer Clock Precision
 // 8 bytes of zero for Root Delay & Root Dispersion
 packetBuffer[12]  = 49;
 packetBuffer[13]  = 0x4E;
 packetBuffer[14]  = 49;
 packetBuffer[15]  = 52;

 // all NTP fields have been given values, now
 // you can send a packet requesting a timestamp:

 udp.beginPacket(address, 123); //NTP requests are to port 123
 udp.write(packetBuffer, NTP_PACKET_SIZE);
 udp.endPacket();

 u8g2.begin();
 }
                                  //LOOP
 
 void loop()
 {
 char hours;
 char minutes;
 char seconds;

// get a random server from the pool
WiFi.hostByName(ntpServerName, timeServerIP); 

sendNTPpacket(timeServerIP); 

// send an NTP packet to a time server
// wait to see if a reply is available
delay(1000);

int cb = udp.parsePacket();
if (!cb) {
Serial.println("no packet yet");
}
else {
Serial.print("packet received, length=");
Serial.println(cb);

// We've received a packet, read the data from it
udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer
//the timestamp starts at byte 40 of the received packet and is four bytes,
// or two words, long. First, esxtract the two words:
unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);


// combine the four bytes (two words) into a long integer
// this is NTP time (seconds since Jan 1 1900):
unsigned long secsSince1900 = highWord << 16 | lowWord;
Serial.print("Seconds since Jan 1 1900 = " );
Serial.println(secsSince1900);

// now convert NTP time into everyday time:
Serial.print("Unix time = ");
// Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
const unsigned long seventyYears = 2208988800UL;
// subtract seventy years:
unsigned long epoch = secsSince1900 - seventyYears;
// print Unix time:
Serial.println(epoch);


// print the hour, minute and second:
minutes = ((epoch % 3600) / 60);
minutes = minutes + MM; //Add UTC Time Zone

hours = (epoch  % 86400L) / 3600;    
if(minutes > 59)
{      
  hours = hours + HH + 1; //Add UTC Time Zone  
  minutes = minutes - 60;
}
else
{
  hours = hours + HH;
}

Serial.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)

Serial.print(hours,DEC); // print the hour (86400 equals secs per day)
Serial.print(':');


if ( minutes < 10 ) {
  // In the first 10 minutes of each hour, we'll want a leading '0'
  Serial.print('0');
}    
Serial.print(minutes,DEC); // print the minute (3600 equals secs per minute)
Serial.print(':');

seconds = (epoch % 60);
if ( seconds < 10 ) {
  // In the first 10 seconds of each minute, we'll want a leading '0'
  Serial.print('0');
}
Serial.println(seconds,DEC); // print the second
}
// wait ten seconds before asking for the time again
delay(10000);
}

{
u8g2.setFont(u8g2_font_ncenB14_tr);
u8g2.firstPage();
do {
u8g2.setCursor(0, 20);
u8g2.print(hours,DEC);
u8g2.setCursor(33, 20);
u8g2.print(minutes,DEC);
} 
while ( u8g2.nextPage() );
}

//This is a code to display ntp time using Nodemcu

#include <ESP8266WiFi.h>
#include <WiFiUdp.h>
#include <Arduino.h>
#include <U8g2lib.h>

#ifdef U8X8_HAVE_HW_SPI
#include <SPI.h>
#endif
#ifdef U8X8_HAVE_HW_I2C
#include <Wire.h>
#endif

U8G2_SH1106_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, /* reset=*/U8X8_PIN_NONE);

char ssid[] = "123456";     //  your network SSID (name)
char pass[] = "123456";     // your network password

//Your UTC Time Zone Differance  India +5:30
char HH = 5;
char MM = 30;

unsigned int localPort = 2390;      // local port to listen for UDP packets

//* Don't hardwire the IP address or we won't get the benefits of the pool.
//* Lookup the IP address for the host name instead */

//IPAddress timeServer(129, 6, 15, 28); // time.nist.gov NTP server

IPAddress timeServerIP; // time.nist.gov NTP server address

const char* ntpServerName = "time.nist.gov";

const int NTP_PACKET_SIZE = 48; // NTP time stamp is in the first 48 bytes 
// of the message

byte packetBuffer[ NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing 
//packets

// A UDP instance to let us send and receive packets over UDP
WiFiUDP udp;


                              //SETUP



void setup()
{
Serial.begin(115200);
Serial.println();
Serial.println();

// We start by connecting to a WiFi network
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.mode(WIFI_STA);
WiFi.begin(ssid, pass);

while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");

Serial.println("WiFi connected");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());

Serial.println("Starting UDP");
udp.begin(localPort);
Serial.print("Local port: ");
Serial.println(udp.localPort());
}


//  Send an NTP request to the time server at the given address

unsigned long sendNTPpacket(IPAddress& address)
{
Serial.println("sending NTP packet...");
// set all bytes in the buffer to 0
memset(packetBuffer, 0, NTP_PACKET_SIZE);

// Initialize values needed to form NTP request
// (see URL above for details on the packets)
packetBuffer[0] = 0b11100011;   // LI, Version, Mode
packetBuffer[1] = 0;     // Stratum, or type of clock
packetBuffer[2] = 6;     // Polling Interval
packetBuffer[3] = 0xEC;  // Peer Clock Precision
// 8 bytes of zero for Root Delay & Root Dispersion
packetBuffer[12]  = 49;
packetBuffer[13]  = 0x4E;
packetBuffer[14]  = 49;
packetBuffer[15]  = 52;

// all NTP fields have been given values, now
// you can send a packet requesting a timestamp:

udp.beginPacket(address, 123); //NTP requests are to port 123
udp.write(packetBuffer, NTP_PACKET_SIZE);
udp.endPacket();

u8g2.begin();
}
                              //LOOP

void loop()
{
char hours;
char minutes;
char seconds;

// get a random server from the pool
WiFi.hostByName(ntpServerName, timeServerIP); 

sendNTPpacket(timeServerIP); 

// send an NTP packet to a time server
// wait to see if a reply is available
delay(1000);

int cb = udp.parsePacket();
if (!cb) {
Serial.println("no packet yet");
}
else {
Serial.print("packet received, length=");
Serial.println(cb);

// We've received a packet, read the data from it
udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer
//the timestamp starts at byte 40 of the received packet and is four bytes,
// or two words, long. First, esxtract the two words:
unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);


// combine the four bytes (two words) into a long integer
// this is NTP time (seconds since Jan 1 1900):
unsigned long secsSince1900 = highWord << 16 | lowWord;
Serial.print("Seconds since Jan 1 1900 = " );
Serial.println(secsSince1900);

// now convert NTP time into everyday time:
Serial.print("Unix time = ");
// Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
const unsigned long seventyYears = 2208988800UL;
// subtract seventy years:
unsigned long epoch = secsSince1900 - seventyYears;
// print Unix time:
Serial.println(epoch);


// print the hour, minute and second:
minutes = ((epoch % 3600) / 60);
minutes = minutes + MM; //Add UTC Time Zone

hours = (epoch  % 86400L) / 3600;    
if(minutes > 59)
{      
hours = hours + HH + 1; //Add UTC Time Zone  
minutes = minutes - 60;
}
else
{
hours = hours + HH;
}

Serial.print("The UTC time is ");       // UTC is the time at Greenwich //Meridian (GMT)

Serial.print(hours,DEC); // print the hour (86400 equals secs per day)
Serial.print(':');


if ( minutes < 10 ) {
// In the first 10 minutes of each hour, we'll want a leading '0'
Serial.print('0');
}    
Serial.print(minutes,DEC); // print the minute (3600 equals secs per minute)
Serial.print(':');

seconds = (epoch % 60);
if ( seconds < 10 ) {
// In the first 10 seconds of each minute, we'll want a leading '0'
Serial.print('0');
}
Serial.println(seconds,DEC); // print the second
}
// wait ten seconds before asking for the time again
delay(10000);
}

Adding the second block of code (print one) to the main code gives me correct time on the oled screen but only when the ntp receives a packet. Otherwise its some 10 digit number. How do I get rid of the number and keep displaying the time till it is update with a valid newer value. I have attached images of display.

{
u8g2.setFont(u8g2_font_ncenB14_tr);
u8g2.firstPage();
do {
u8g2.setCursor(0, 20);
u8g2.print("hours"));
} while ( u8g2.nextPage() );

{
u8g2.setFont(u8g2_font_ncenB14_tr);
u8g2.firstPage();
do {
   u8g2.setCursor(0, 20);
   u8g2.print("hours"));
   }  
while ( u8g2.nextPage() );