Hi Sumanta,
I haven’t gone deeply through your code, but I found these,
Increase the delay for enable, try some 5ms.
Globally declare LCD_string(void); It dosen’t matter, but a standard.
You can hardwire the R/W pin to ground. Since you are writing only, no need to drive it through your code.
Its not clear what kind of problem you are facing. Are you getting junk values only?