Code does not work!!!

[mathmari]

Hi everybody!!!!
Could you tell me why the following code doesn't work???
That is the code:

#include <stdio.h>
#include <string.h>

void func(char *p1,char *p2){
	char ch;
	while (p1<p2){
		   ch=*p1;
		   *p1=*p2;
		   *p2=ch;
		   p1++;
		   p1--;
	}
}
		  
int main()
{
	char a[8]="VENICE";
	puts(a);
	func(a,a+4);
	puts(a);
	return 0;
}

Thanks in advance!