anIdiotsGuideToProgtest_returning.c

#include <stdio.h>

//x is passed as pointer to memory where actual value is stored
void addOneUsingPointers(int *x) {
  // here we add to the value x is pointing to
  // x is currently pointing at "a" variable in main function
  // this means that we add 1 to "a"
  (*x)++;  // x is address of memory, (*x) is the actual value
}

//x is passed as copy of value
void addWithoutUsingPointers(int x) {
  x++;  //value was added but not returned
}

// x passed as copy of value
// starts with "int" which is type of the value we want to return
int addValueWithReturn(int x) {
  x++;
  return x;
}

int main() {
  int a=0;
  printf("starting value of a: %d\n", a);
  // we pass the pointer to the value "a" instead of the actual value
  // this means that we can modify the "a" variable without using "return"
  addOneUsingPointers(&a);
  printf("one was added to a: %d\n", a);

  // here we pass value to the function, but no modifications can be made within
  // the function, since there is no way for the function to access the actual variable
  // (it has only a copy of it)
  addWithoutUsingPointers(a);
  printf("nothing was added to a: %d\n", a);

  // here we send a copy of variable "a" and use "return" to get the value back from the function
  // the value in "a" is not changed since we do not save the returned value to any other variable
  addValueWithReturn(a);
  printf("value was properly returned but not saved, a: %d\n", a);

  // here we save the returned value back to variable "a" so it is changed and returned correctly
  a = addValueWithReturn(a);
  printf("value properly returned and properly saved, a: %d\n", a);


  return 0;
}