What is the difference of pass by value and pass by reference?

Every variable that you create in your code requires some memory (on RAM) to store its value. For example, when you create an integer in C++, the system reserves 2 bytes in RAM to store the value of the integer. Every variable can be located internally by the system using an address called memory-address (it is a binary number). If you want to pass a variable as a functions argument, there are two ways, it can be done: 1) Pass by value. Here the value of the variable being passed is copied into the function's parameter variable. Example: Suppose we have a function void add(int a, int b); In main function, we call the function such as: int x = 5, y = 6; add(x, y); Now here, when the function is called, the values of x and y (5 and 6) are copied into the function's parameters a and b. This means that if you change the values of a and b inside the function's code, then x and y are not affected. 2) Pass by reference When we pass a variable by reference the address of the variable being passed is copied into the function's parameter. Example: Suppose we have a function void add(int &a, int &b); In main function, if we call it using the same code: int x = 5, y = 6; add(x,y); then, only the reference of x and y will be passed to a and b instead of copying the values. Hence, a and b will use the same memory location of x and y to access or change its values. This means that if you change the value of a inside the function, then it will change the value of variable x of main function. Similarly changing value of b will change y of main. Long answer, but I hope I have managed to explain you the difference. Feel free to contact me if you have any doubts. :) read less

Say I want to share a web page with you. If I tell you the URL, I'm passing by reference. You can use that URL to see the same web page I can see. If that page is changed, we both see the changes. If you delete the URL, all you're doing is destroying your reference to that page - you're not deleting the actual page itself. If I print out the page and give you the printout, I'm passing by value. Your page is a disconnected copy of the original. You won't see any subsequent changes, and any changes that you make (e.g. scribbling on your printout) will not show up on the original page. If you destroy the printout, you have actually destroyed your copy of the object - but the original web page remains intact read less

In pass by value approach, the called function creates another copies of the variables passes as arguments. In this approach, the values of the original variables remain unchanged. However, we come across situations where we need to change the values of the original variables. Then the values may b passed by reference read less

1) In pass by value, the value of the arguments (actual parameters) are copied to the formal parameters whereas in pass by reference, the address of the arguments (actual parameters) are copied to the formal parameters. 2) In pass by value, changes to the formal parameters won't alter the value of the arguments (actual parameters) whereas in pass by reference, changes to the formal parameters alter the value of the arguments (actual parameters) read less