how to write a function in c for mysql

[LookingBeyond99]

I was trying to figure out how would you write a function in MySQL using C. I saw that theres a CREATE FUNCTION syntax but am confused on how to compile and write a C function.

For example if I wanted to write a function that added an extra period after every period and called it ADD_PERIOD() how would I do that.

Example:

x = "joe runs far."
SQLSTRING = "SELECT * from Story where Sentence = '"+ADD_PERIOD(x)+"'";

this would return. joe runs far..

Thanks