Write a program to determine if an input character string is of the form
xCy
where x is a string consisting of the letters ’A’ and ’B’, and where y is the reverse of x (that is, if x="ABABBA", y must equal "ABBABA"). At each point, you may read only the next character of the string.

void main()
{
	element c, e;
	stack s;
	int valid;

	valid=1;

	s=CreateStack();
	do{
		c=getchar();
		if(c!='C')
			Push(&s,c);
	}while(c!='C');

	while(Top(s,&e)==1 )
	{
		Pop(&s); 
		c=getchar();
		if(c!=e)
			valid = 0;
	}

	if(!isEmptyStack(s))
		valid=0;

	if(valid==1)
		printf("Valid Expression");
	else
		printf("Invalid Expression");

	getch();
	return 0;
}