C why the while operator is code example

Example 1: WHILE loop in c

while( a < 20 ) {
      printf("value of a: %d\n", a);
      a++;
   }

Example 2: do-while in c

#include <stdio.h>
int main()
{
	int j=0;
	do
	{
		printf("Value of variable j is: %d\n", j);
		j++;
	}while (j<=3);
	return 0;
}