Arduino function

Sometimes i so when caling a funtion ,by given its parameteres ,they give parameter value stored variable name with "&" symbol.why that?

It's most likely the address-of operator:
http://www.cplusplus.com/doc/tutorial/pointers/
https://en.cppreference.com/w/cpp/language/operator_member_access#Built-in_address-of_operator

Pieter

It means "pass by reference" Normally, a copy of the variable is passed into a function and the function can do whatever it wants and when it returns, the original variable is unchanged. When you pass by reference, the function can actually change the value of the variable.

blh64:
It means "pass by reference" Normally, a copy of the variable is passed into a function and the function can do whatever it wants and when it returns, the original variable is unchanged. When you pass by reference, the function can actually change the value of the variable.

OP asked about "when caling a funtion", so I think he meant the address of operator.

But he should definitely ask a clearer question, it's very hard to understand what he actually means.

Always give an example for us to work with.