c++ - Why is my programs outputting values , 250? -

i new c++. having difficulty pointers, , cannot grasp full understanding of how pointers work. have experimented different programs utilising pointers dont understand why outputs way does. please me understanding why cout outputs values 250. understand how processed values of reference value , both 12's 250?? can explain?? below code

#include <iostream>  using namespace std;  int main(){    int firstvalue = 12 , secondvalue = 6 ;    int *ptr;    ptr = &firstvalue; //address of firstvalue assigned ptr   ptr = &secondvalue;    *ptr = 250; // value pointed ptr = 250    cout << ptr << "\n";   cout << firstvalue << "\n";   cout << secondvalue << "\n";   cout << firstvalue << "\n"; } 

program output :

address value // cant remember 12 250 12 

int firstvalue = 12 , secondvalue = 6 ; 

firstvalue holds 12. secondvalue holds 6. (bad habit imho. avoid comma, declare 1 variable per statement only. makes easier avoid errors later on when start declaring multiple pointers...)

int *ptr; 

ptr pointer-to-int holding indeterminate value @ point.

ptr = &firstvalue; //address of firstvalue assigned ptr 

now ptr holds address of firstvalue.

ptr = &secondvalue;  

now ptr holds address of secondvalue.

*ptr = 250; // value pointed ptr = 250 

ptr -- holding address of secondvalue -- gets dereferenced (that asterisk * here), , result -- secondvalue -- gets new value assigned (250).

now firstvalue holds 12, , secondvalue holds 250.

cout << ptr << "\n"; cout << firstvalue << "\n"; cout << secondvalue << "\n"; cout << firstvalue << "\n"; 

and gets printed:

address value // cant remember 12 250 12 

works expected.