C; Call by Value / Call by Address

#include<stdio.h>

void input(int p){
   p=20;
}

void swap(int *p){
   *p=10;
}

void main(void){
   int a = 5;
   printf("Original input: %d\n",a);

   input(a);
   printf("Result of input: %d\n", a);

   swap(&a);
   printf("Result of swap: %d\n",a);
}