What Is Difference Between Call-by-value And Call-by-reference?

The call by value is used in c and the changes made to the variables of the callled function are not reflected back to the calling function .....however call by refrence uses addresses and pointers and the changes made to the variables in the called function are reflected back to the calling function

Explain the difference between call by value and call by reference in c++ with suitable example

In call by value the value of the variable passer to the function and it does not return any value
In call by reference the  address of the variable is passed to the function and therefore any change made in the function is permanent since it affects the memory location

Call by reference is used to reflect the modification of value in actual parameter which has been assigned as an argument to a function after coming back from the called function. It is used in VB with the keyword ByRef.
Call by value is used to secure the value of the actual parameter which has been used as an argument to a function after coming back to to calling function. VB provide this service with ByVal keyword