Why strcmp equals zero

I followed Hammer's tutorial on Comparing Strings, but one thing I don't understand.

Code:

if(strcmp(foo, bar) == 0)
  puts("Strings equal");
else
 puts("Strings not equal");

Why compare these strings to zero. I know that in boolean 0 is false and 1 is true. I have to say that these tutorials are very good for beginners.

Thanks.

string comparison starts with the first character and goes on till a character differs or one of the strings gets completed
coonsider strcmp(s1,s2)
if strcmp(s1,s2) == 0 => s1==s2
if strcmp(s1,s2) <0 => s1<s2
ifstrcmp(s1,s2) > 0 => s1>s2

oh and the value strcmp returns is the diff. betwn. the value of the corres. characters of the strings. //pls. verify this

Somehow I got the code for this (and many other c functions)

-edit-
Ok, they're all the source code for C functions....in C. Some of the functions are written in assembly, but I don't feel like finding the one's I've seen. It's just nice to see how they did the actual functions written out.

anyways

Code:

     
     /***
     *strcmp - compare two strings, returning less than, equal to, or greater than
     *
     *Purpose:
     *	   STRCMP compares two strings and returns an integer
     *	   to indicate whether the first is less than the second, the two are
     *	   equal, or whether the first is greater than the second.
     *
     *	   Comparison is done byte by byte on an UNSIGNED basis, which is to
     *	   say that Null (0) is less than any other character (1-255).
     *
     *Entry:
     *	   const char * src - string for left-hand side of comparison
     *	   const char * dst - string for right-hand side of comparison
     *
     *Exit:
     *	   returns -1 if src <  dst
     *	   returns  0 if src == dst
     *	   returns +1 if src >  dst
     *
     *Exceptions:
     *
     *******************************************************************************/
     
     int __cdecl strcmp (
     		const char * src,
     		const char * dst
     		)
     {
     		int ret = 0 ;
     
 		while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
     				++src, ++dst;
     
     		if ( ret < 0 )
     				ret = -1 ;
     		else if ( ret > 0 )
     				ret = 1 ;
     
     		return( ret );
     }

To reiterate what alvarorahul said:

strcmp() compares the strings one character at a time. If the characters match it goes on to the next character. Once it finds a difference it subtracts the character from string2 from the character from string1.

So given:

Code:

char s1[] = "My name is Bob";
char s2[] = "My name is Billy";

It will compare "My name is B" from both strings and then read o from s1 and i from s2 and then returns the value of o-i. If the value returned is < 0 then s1 is less than s2, if the value returned is > 0 then s1 is greater then s2. So by default (only range left) 0 means they are the same.

strcmp is really helpful in sorting algorithms.