What is the difference between copying a value and copying a reference in c language?

In any language, if you pass a variable's reference, then you can change the value of the referenced variable with the code that obtained the reference.





If you pass the value of a variable, the code which obtains it cannot change the value of the original variable.





For example:





int x = 100;





void myfunction(%26amp;int z){


//some code


z = 30


}





would make x = 30!





If you do this:





void myfunction(int z) {


//some code


z = 30


}





x still equals 100.

What is the difference between copying a value and copying a reference in c language?
Copying a value is simply assign the variable to another one


eg:int x = 10;


int y = x /* copy of x is y . Now y= 10 */





Copying a reference means copy the address location of the variable


eg: int x = 10;


int *y = %26amp;x /* here y is assigned with a place holder (addtress location) only