explain call by value and call by reference with example

Example: call by reference

//Call By Reference

#include<stdio.h>
void function(int *, int *);       //function declaration
int main()
{
	int a,b;
    
    printf("Enter first number: ");
    scanf("%d",&a);
    printf("Enter second number: ");
    scanf("%d",&b);
    
    function(&a,&b);    //passing the address of both the variables( CALL BY REFERENCE)

}
void function(int *p,int *q)     //function defination
{
   printf("printing variables from function a=%d b=%d",*p,*q);
}
//code by Dungriyal..