I didn't understand how the variable in function declaration and function definition not same pass by value or reference, can you explain please and trace the code ? in c++

2. using namespace std; 3. void f1 (int\& a, int b, int\& c ); 4. int main () 5. \{ 6. int x=1,y=3,z=2; 7. f1(x,y,z); 8. cout "x="x