change the value of constant variable in c++

 #include  
 int main()  
 {  
 int *ptr;  
 const int val = 20;  
 clrscr();  
 printf("Value is: %d\n", val);  
 ptr=(int*)&val;  
 *ptr = 2000;  
 printf("Value is: %d\n", val);  
 getch();  
 return 0;  
 }