how does 2b 2boperator works in c 2b 2b

1#include <stdio.h>
2int main() {
3   int var1 = 5, var2 = 5;
4
5   // 5 is displayed
6   // Then, var1 is increased to 6.
7   printf("%d\n", var1++);
8
9   // var2 is increased to 6 
10   // Then, it is displayed.
11   printf("%d\n", ++var2);
12
13   return 0;
14}