K&R problem !! String concatenation :(

Here is another problem from K&R , I have been sittin with it for 4 hours

This program tried to concatenate two strings. It aint doin it

Code:

---


#include "stdio.h"

int  str_cat(char *, char *);

int main()
{
        char *str1 = "saguna";
        char *str2 = "karan";
        str_cat(str1,str2);
        return 0;
} //main closes

int  str_cat(char *st1, char *st2)
{
        for(; *st1 != '\0'; st1++)
        {
                if(*st1 == '\0')
                {
                        printf("check ");          //not goin in if statement, it goes till s
                        for(;*st2 != '\0';st2++)
                        {
                        *st2 == *st1;
                        }
                        printf("The value of *st2=\n\n\n\n\n%c",*st2);
                        //return *st2;
                }
                else
                {
                        printf("\nsomethings wronng\n");
                }
        }
} //str_cat closes

---

Kindly help. I have tried my best :confused:

You will really need to use arrays here -- at least for str1 -- so you can write to it.

Code:

---

        char *str1 = "saguna";
        char *str2 = "karan";

---

Re-examine your logic here.

Code:

---

        for(; *st1 != '\0'; st1++)
        {
                if(*st1 == '\0')
                {
                        printf("check ");          //not goin in if statement, it goes till s
                        for(;*st2 != '\0';st2++)
                        {
                        *st2 == *st1;
                        }
                        printf("The value of *st2=\n\n\n\n\n%c",*st2);
                        //return *st2;
                }
                else
                {
                        printf("\nsomethings wronng\n");
                }
        }

---

You're only in the loop if you haven't reached the null terminator. In the loop you check to see if you are at the null terminator, which won't happen.

String concatenation: find the end of the current destination (the null terminator), then copy the source to the end of the current destination until you reach the end of the source.

[edit]And do the #include like this.

Code:

---

#include <stdio.h>

---

Code:

---

#include "stdio.h"

void str_cat(char *, char *);

int main()
{
        char *str1 = "saguna";
        char *str2 = "karan";
        str_cat(str1,str2);
        return 0;
} //main closes

void str_cat(char *s1, char *st2)
{      char *st1=s1;
        for(; *st1 != '\0'; st1++);

                if(*st1 == '\0')
                {
                        printf("\ncheck ");         
                        for(;*st2 != '\0';)
                        {
                        *st1++ = *st2++;
                        }
                        *st1='\0';
                        printf("The value of *s1=%s",s1);
                        //return *st2;
                }


} //str_cat closes

---

this code is according to your logic.
check points=>
1.for statement is ended by semicolon.because it will never be in if statement of your for loop.
2.you have to add str2 in str1.so str1 will be in left of assignment operator.assignment is done by = operator,not by ==.
3.to end the str1.you have put a null character '\0'
4.your function returns nothing

Your code contained some silly mistake thats it.well best of luck for the next time

Just to make Dave's answer even clearer

char *str1 = "saguna";
Should be
char str1[100] = "saguna";
If you want something you can actually append data to.

"string" constants like this are typically in read-only memory. As soon as you try and modify them, you'll get a segmentation fault.

What's wrong with

Code:

---

while(*from) *to++ = *from++;
*to = 0;

---

Which can really just be:

Code:

---

while( *to++ = *from++ );

---

There's no point in not copying the null over. This is also fine, because you're allowed to point one past the end of an array for comparison only. Although this alone is more of a strdup then a strcat, so you'd want to advance to the end of 'to' first.

So, if we hide warnings with parenthesis, we should have something like this:

Code:

---

while( *to++ );
to--;
while( (*to++ = *from++) );

---

Quzah.

Quote:

---

more of a strdup then a strcat

---

Do you mean strcat?

Well, either way, it seems a little simpler than what was originally posted.

Quote:

---

Originally Posted by dwks

Do you mean strcat?

---

And do you mean strcpy?

Quote:

---

Originally Posted by dwks

Do you mean strcat?

Well, either way, it seems a little simpler than what was originally posted.

---

No. I said what I meant. Your code as really just duping the origional into the new buffer. Thus, it's more of a strdup than a strcat.

Quote:

---

Originally Posted by itsme86

And do you mean strcpy?

---

I suppose it's really more of a strcpy than a strdup, since it isn't actually allocating any more space, it's just filling another buffer.

But in any case, it (dwks' code) wasn't what the origional had intented, as far as I saw it:

Quote:

---

Originally Posted by karanmitra

Here is another problem from K&R , I have been sittin with it for 4 hours

This program tried to concatenate two strings. It aint doin it

Code:

---

#include "stdio.h"

int  str_cat(char *, char *);

---

---

Though it was a fragment, so had they advanced to the end of destination string first, it would have done the trick.


Quzah.

just try out this so u could find the answer for your previous problem

Code:

---

#include<stdio.h>
main()
{
char *s1="Hello";
for(;*s1!='\0';s1++)
printf("%s",s1);
}

---

The Logic could be like this

Code:

---

str_cat(char *s1,char *s2)
{
char *s3;
s3=s1;
for(;*s1!='\0';s1++);
for(;*s2!='\0';s2++,s1++)
*s1=*s2;
*s1='\0';
printf("%s",s3);
}

---

Try it out.