Problem Returning Value

**CProgramming11** · 11-20-2010

Hi guys, I've been trying to get this function to work but nothing seems to be doing it. I'm basically comparing two strings: if they have no identical letters in them, I return true, if they have one or more letters common to both strings I return false. It works for the true cases and seems to work for the false cases. The problem is, instead of returning false it returns a random number such as 41256. Can anyone point out where the problem is?

Code:

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

bool i........eroPair (char *a,char *b)
    {
        int i,j;
        for (i=0;i<strlen(a);i++)
    {   for (j=0;j<strlen(b);j++)
        {if(*(a+i)==*(b+j))
        return false;
        else
        ;
        }
    }
       return true;
    }



int main(void)

{
 char *string1="ABCD";
 char *string2="EFGH";
 i........eroPair(string1,string2);
}

**quzah** · 11-20-2010

He said "doing it".

Quzah.

**CProgramming11** · 11-20-2010

Nice

**CProgramming11** · 11-20-2010

Also

"Array names are not pointers, so you cannot increment them.

Quzah. "

Lol.

**quzah** · 11-20-2010

Sorry, I couldn't help myself.

As to your second post, it's true. I'm not sure what relevance that has here, but you can't increment a pointer name. You are apparently taking this out of the context of a thread comparing pointers to arrays. Anyway, I'm right.

Edit. Nevermind, you're basically doing a strchr loop.

Code:

bool foo( char *s1, char *s2 )
{
    while( s1 && *s1 )
    {
        char *p = s2;
        for( p = s2; *p; p++ )
            if( *s1 == *p ) return false;
        s1++;
    }
    return true;
}

Your example never actually does anything with your return value though.

Quzah.

**CProgramming11** · 11-20-2010

Okay, I see what you're getting at but I don't understand why it isn't returning false and instead is returning '4206592'. I also tried making a function to determine if a string is symmetric, it also does the same thing (works properly for true cases, returns '4206592' for false cases).

**CProgramming11** · 11-20-2010

Your function also works but still it returns that 420...number.

**quzah** · 11-20-2010

Make a small example to test it:

Code:

#include<stdio.h>
#include<stdbool.h>
bool retfalse( void ) { return false; }
int main( void )
{
    printf( "false is %d, and retfalse() gives %d\n", (int) false, (int) retfalse() );
    return 0;
}

Your example isn't actually doing anything with a return value, so I can't tell why you're getting the value you aren't expecting.

Quzah.

**CProgramming11** · 11-20-2010

Okay, I tried using the result in a simple if statement in the main function and it works properly. I guess it doesn't matter why it was returning 420.....

Problem averted!

**~~CommonTater~~** · 11-21-2010

You could make your life easier by having it return 0 for false, 1 for true.

The bizarre number, which looks like a pointer address, will work as long as your are comparing false to false but it's not going to work with the ! operator and may cause other logic problems in your code.

You should open the stdbool.h header and have a look... This is the standard one...

Code:

#ifndef _STDBOOL_H
#define _STDBOOL_H

/* stdbool.h - C99 standard header */

/* macros */
#define bool  _Bool
#define false  0
#define true  1
#define __bool_true_false_are_defined  1

#endif /* _STDBOOL_H */

**CProgramming11** · 11-21-2010

Funny enough, returning 0 also returns that 420...value. By this I mean i run the original code I posted and the run screen will show 'Process returned 4206592'.

When I call the function inside an if statement in the main program it works properly. i.e. if the function returns false, it goes to my else statement if not it does the if portion. Weird.

**laserlight** · 11-21-2010

Originally Posted by CProgramming11

Funny enough, returning 0 also returns that 420...value. By this I mean i run the original code I posted and the run screen will show 'Process returned 4206592'.

I think that you are confusing the return value of the function with the exit status of the program (process).

I suggest that you compile and run this program, which is a cleaned up version of what you posted originally:

Code:

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

bool foo(const char *a, const char *b)
{
    size_t i, j, len_a = strlen(a), len_b = strlen(b);
    for (i = 0; i < len_a; i++)
    {
        for (j = 0; j < len_b; j++)
        {
            if (a[i] == b[j])
                return false;
        }
    }
    return true;
}

int main(void)
{
    const char *string1 = "ABCD";
    const char *string2 = "DEFGH";
    printf("%d\n", foo(string1, string2));
    return 0;
}

Is the output 0? If so, there is no problem.

**CProgramming11** · 11-21-2010

Yes that program works fine.

You're right, I just confused the return value for the exit status. I'm used to seeing the return value as the exit status of the program. Newb mistake. Thanks

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