Reverse of string using pointers

[sandeep n]

I am not getting reverse string using following code,

can u explain where i did mistake and correct it

with regards
sandeep

code-->>>

#include<stdio.h>
#include<string.h>
main()
{
	char s1[100],s2[100],*p,*q;
	gets(s1);
	p=s1;q=s2;
	while(*p!='\0')
		p++;
	while(p>=&s1[0])
	{
		*q++=*p--;
	}
	*q='\0';
	printf("\ngiven string--->%s\n",s1);
	printf("\nreverse string--->%s\n",s2);
}

[mac11]

I think the first thing that happens is that you copy the NULL into s2[0] so when you try to print s2 nothing comes out.

A couple of other good habits:
1. use fgets or getline instead of gets http://www.crasseux.com/books/ctutorial/gets.html
2. It's a good habit to always initialize variables - I'm referring specifically to s1 and s2.
3. you don't need the first loop to find the end of s1, you can use strlen for that

[sandeep n]

You know that
*q++=*p--;
reduces to
*q=*p;
q++;p++;
for the 1st instant of the loop q points to first element of the s2 and s1 points to last element of the s1
*q=*p for the first instant should copy last element of s1 into first element of s2

Is not it...

Please clarify clearly

[whodgson]

After the pointers are positioned at each end of the SAME string just swap them (what they are pointing to) using the swap() function defined in the header <algorithm>.

[sandeep n]

Good Idea

but what's the wrong in the code?

[stereomike]

Good Idea

but what's the wrong in the code?

s2[0] is '\0'
s2+1 will be the reversed string.

Put p--; in between the two while loops.