#include <stdio.h>

void echange_1(int x, int y) {
  int tmp;

  tmp = x;
  x   = y;
  y   = tmp;
}

void echange_2(int *x, int *y) {
  int *tmp;

  tmp = x;
  x   = y;
  y   = tmp;
}

void echange_3(int *x, int *y) {
  int tmp;

  tmp = *x;
  *x  = *y;
  *y  = tmp;
}

void echange_4(int *x, int *y) {
  int *tmp;

  *tmp = *x;
  *x   = *y;
  *y   = *tmp;
}

// Expliquer de façon détaillée et justifiée ce qu'on obtient à l'exécution.

int main(void) {
  int a = 1, b = 2;
  echange_1(a, b);
  printf("a = %d, b = %d\n", a, b);

  a = 1, b = 2;
  echange_2(&a, &b);
  printf("a = %d, b = %d\n", a, b);

  a = 1, b = 2;
  echange_3(&a, &b);
  printf("a = %d, b = %d\n", a, b);

  a = 1, b = 2;
  echange_4(&a, &b);
  printf("a = %d, b = %d\n", a, b);

  return 0;
}