12c sending numeric data (arduino to NodeMCU)

Step 1: understand that I2C (and SPI and UART and similar) transfer/exchange values but put no interpretation on what those values mean. Typically I2C will transfer bytes.
Step 2: you need to determine how you want to use the I2C mechanism to transfer your 'numbers'. Perhaps the numbers are 8, 16 or 32 bit integers in which case you use I2C to transfer 1, 2 or 4 bytes respectively. Perhaps the numbers are strings (as you suggest in your question) in which case you send however many bytes (assuming each character in the string is a byte and not UTF-16 and the like) make up the string - also remembering you may need some additional means to signal that the last byte has been sent such as a NULL value or have all of the bytes in some order within a single I2C transaction.
Step 3: write the appropriate code in your NodeMCU and your Arduino in whatever language you want to use in each.
Susan

I used arduino slave and Nodemcu master codes from the following tutorial. The two are sending test messages. Nodemcu is sending "Hello Arduino" and arduino is sending "Hello Nodemcu". The communication is running perfectly. both are receiving the test properly.
But when I make a string and save it in a String variable, it is not functioning. If the above text in quotes is a string, why it is not able to use the string I make.
If the three numbers are stored in int a, int b and int c I construct a string
String s = String (a) + String (b) + String (c)
this is not working kindly advise how to handle this

https://www.electronicwings.com/nodemcu/nodemcu-i2c-with-arduino-ide

What does "not functioning" mean? Is there smoke and flames? Are you getting any data?

What does "not functioning" mean? Is there smoke and flames? Are you getting any data?

What does "not functioning" mean? Is there smoke and flames? Are you getting any data?

Show us YOUR code please.
Susan