explain xkcd:Sandbox

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b
Name
Born	Unknown

#include <cstdio>
int a[3]={0,0,0};
void acase(int b){
	if(b>=0)printf("case %d:",b);
}
void dcase(int d,int m=0){
	printf("\t\t\t\t");m?printf("  "):0;acase(a[0]+d);acase(a[1]+d);acase(a[2]+d);m?printf("\n"):printf("printf(\"2$\");break;\n");
}
int main() {
	dcase(9,1);
	dcase(0);
	dcase(10,1);
	dcase(1);
	dcase(2,1);
	dcase(3,1);
	dcase(6,1);
	dcase(7,1);
	dcase(11,1);
	dcase(12,1);
	dcase(17,1);
	dcase(18);
	dcase(14,1);
	dcase(4);
	dcase(15,1);
	dcase(5);
	dcase(8);
	dcase(13);
	dcase(19);
	dcase(16,1);
	dcase(20);
	return 0;
}