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c++pointersincrement

Why does this code have different outputs if pointers are incremented differently c++

#include <iostream>
using namespace std;
int main() {
  int num=10;
  int *ptr=NULL;
  ptr=&num;
  num=(*ptr)++; //it should increase to 11
  num=(*ptr)++; //it should increase to 12 but im getting 10
                //if i dont initialize num and just use (*ptr)++ it gives me 11
  cout<<num<<endl;
    return 0;
}

I want to know why is this happening and why am I getting 10 as output.

Solution

  • (*ptr)++ increases num to 11 but returns its previous value (10), because the ++ is postfix.

    So with num = (*ptr)++, you are temporarily increasing num to 11, but then (re)assigning it with 10.