Bad style, side-effects, value-returning using c++

#include <iostream.h>

int counter = 0;

int add (int&, int&);

void main () {
  int i, j, sum;

  i = 7; j = 17;
  sum = add(i,j);
  cout << "counter = " << counter << ", i = " << i << ", j = " << j 
    << ", sum = " << sum << endl;

  i = 7; j = 17;
  sum = add(i,j);
  cout << "counter = " << counter << ", i = " << i << ", j = " << j 
    << ", sum = " << sum+i+j+counter << endl;

  i = 7; j = 17;
  sum = i+j+counter;
  cout << "counter = " << counter << ", i = " << i << ", j = " << j 
    << ", sum = " << sum+add(i,j) << endl;

  i = 7; j = 17;
  sum = add(i,i);
  cout << "counter = " << counter << ", i = " << i << ", j = " << j 
    << ", sum = " << sum << endl;
}

int add (int& a, int& b) {
  int temp, sum;

  sum = a+b;
  temp = a;
  a = b+1;
  b = temp+1;
  counter = counter + 1;
  return(sum);
}