I am using big font library and when i am trying to display some other custom character it is replaced by one of big font character how to solve this, so that big font and my custom character work together.
Are you using a display like the 1602 or 2004 LCD displays?
If so a guess would be that you can not change any font character on the fly without changing all of the font characters of that character location that are already on the display.
I think it works like this...
If you program a character 'A' at location 0x01 and a different one 'B' at location 0x02 for example, and display those two characters you'll see:
on the display.
If you then change the character data for that same location 0x01 which was the character 'A' to the character 'C' and then without doing anything else print that character you'll see this:
So what happened to the 'A' ?
I think what happens is it maps all of the characters onto the display dynamically so that any character that is changed in the program changes in the display right away, on the next display refresh.
So what this means is if you have say 8 characters to work with and you expect to display them and keep them on the display, then they need to stay the same codes throughout the time they are on the display, or else they will change when they are reprogrammed in the program code.
This is just a guess, but that's the way my 1602 worked anyway. I think i had to do a display reset too or something.