/*
 * To reverse a sentence without reversing the letters in its words using a recursive function
 * @author-Karan Narain(karan@iitk.ac.in)
 *
*/
#include <stdio.h>
#include <string.h>
/*
 * rev takes 2 parameters-A points to the next word in the sentence
 * B points to the destination for the reversed string
 */
void rev(char *A,char *B)
{
	int first=0;	//used to check if this is the first call
	char buffer[80],*x,*y,*z,*buf;
	x=A;
	y=B;
	if(*y==' ')	//' ' is the chosen initial value stored in passed B,so this will be true only in first call
	{
		first=1;
		*y='\0'; //change the value in B to an empty string
	}
	buf=buffer;
	//loop to store a word in buffer
	while(*x!=' ' && *x!='\0')
	{
		*buf=*x;
		buf++;
		x++;
	}
	*buf='\0';  //Null-terminate the word stored in buf
	if(*x!='\0')
	/*
	 * Make a recursive call passing the remaining sentence and the same destination pointer
	 * The idea is to store one word in buf in every recursive call and when the last word has been stored,start putting them in the destination in reverse order
	 */
	rev(x+1,y); 

	while(*y!='\0') //proceed to the end of the words stored in the destination till now
	y++;
	buf=buffer;     //Make buf point to start of buffer again
	//put the word in buf into the destination
	while(*buf!='\0')
	{
		*y=*buf;
		y++;
		buf++;
	}
	*y='\0';
	//If this was the first call made,it would be the last to end and so the reversed sentence should be displayed here
	if(first==1)
	{
			
		printf("\nThe reversed sentence is ");
		puts(B);
	}
	//If this was not the first call,then there are more words to follow and so a space is inserted into the destination and it is then Null-terminated
	else
	{
		*y=' ';
		y++;
		*y='\0';
	}
}
int main()
{
	char A[200],B[200];
	printf("Enter the sentence\n");
	gets(A);
	//Choose an initial value for the destination
	B[0]=' ';
	rev(A,B);
	return 0;

}