Exercise 1

Write a function which changes the value of a:

#include <stdio.h>
void change_a(...)
{
  ...
}

int main()
{
  int a;
  change_a(...);
  printf("The value of a is %d", a);
  return 0;
}

We need to pass the address of a using the addressof operator: &.

#include <stdio.h>
void change_a(int *p_a, int value)
{
  *p_a = value;
}

int main()
{
  int a;
  change_a(&a, 42);
  printf("The value of a is %d", a);
  return 0;
}

Write a function which does NOT change the value of a:

#include <stdio.h>
void dont_change_a(...)
{
  ...
}

int main()
{
  int a;
  dont_change_a(...);
  printf("The value of a is %d", a);
  return 0;
}

We can pass the value of a as usual since it will be copied into the function scope.

#include <stdio.h>
void dont_change_a(int a, int value)
{
  a = value;
  printf("In the functio scope, the value of a is %d", a);
}

int main()
{
  int a = 24;    // We need to initialise the value of a before printing it 
  dont_change_a(a, 42);
  printf("The value of a is %d", a);
  return 0;
}