And now i will show u the difference between by value and by reference in c++ by the below example and you can test it to understand more and more

#include <iostream>
using namespace std;

//declaration the function

/**
 - value - passing parameter by value
 - @param int
**/
void value(int);

/**
 - reference - passing parameter by reference
 - @param int& - number to be incremented
**/
void reference(int&);

int main(){
int num = 5;
value(num);
cout << " the value func result is : " << num << endl;
reference(num);
cout << " the reference func result is : " << num << endl;
return 0;
}

//defination the function
void value(int num){

num+=2;
}
void reference(int& num){

num+=2;
}