String Concat

Hi,
I am trying to write a program to concat two strings. Its a simple one, but i am unable to indentify the error. Please help.

#include <stdio.h>

int main()
{
char s1[80],s2[80],s3[80];
int len1,len2;
printf("Enter the first string\n");
scanf("%s",&s1);
printf("\nEnter the second string to be appended to the first\n");
scanf("%s",&s2);
len1=strlen(s1);
len2=strlen(s2);
xstrcmp(s1,s2,len1,len2);
}

xstrcmp(char *s1,char *s2,int len1,int len2)
{
int i;
s1=s1+len1;
for(i=0;i<=len2;i++)
{
*s1=*s2;
s1++;
s2++;
}
printf("\nThe concatenated string is %s",s1);
getch();
}

Should
scanf("%s",&s1);
be
scanf("%s",s1);?
as a string is a pointer unless given an array ref

Also some error check
ie if(len1+len2<=(80-1))//if both strings are less than the total space

I'm not sure about
s1=s1+len1

how about
char *pS1,*pS2;

pS1=s1[len1];//set to the end inc '\0'
pS2=s2[0];//set to start

No it still doesnt work, even without '&'.

At first let me tell you, that you must get a book .

Now let's go to the errors:

1) You must include "<conio.h>" if you want to use "getch()" command and "<string.h>" if you want to use "strlen" command;

2) you need a prototype for you function. In this case it would be "void xstrcmp (char *s1, char *s2, int len1, int len2);";

3) main function must return 0 and you do not need s3[80];

4) when you are entering string in scanf you must always write it like that "scanf("%s", string);";

I write my own function for this. It's a little longer but it works.
Try it !

Code:

void xstrcmp(char *s1, char *s2, int len1, int len2) 
{ 
	char ConStr[80], *PtrConStr;

	if (len1 + len2 < 80) // this is for error checking, two strings together must not exceed 79 characters
	{
		PtrConStr = ConStr; // you must "connect" pointer with the string (this is a direction of a pointer)
		while (*s1 != '\0') // with this while loop I write from s1 into ConStr
		{
			*PtrConStr = *s1;
			PtrConStr++;
			s1++;
		}
		*PtrConStr = '\0'; // you must add this - it is defined as the end of the string
		while (*s2 != '\0') // and with this while loop I write from s2 into ConStr
		{
			*PtrConStr = *s2;
			PtrConStr++;
			s2++;
		}
		*PtrConStr = '\0'; 
		printf("\nThe concatenated string is %s", ConStr);
	}
	else printf("\nStrings are too long.");
}

Thanx a lot for the help once again. I am trying to read books but none of them give information in detail. Is there any book which goes into details(depth).

mhm, pretty inefficient...

try this one:

Code:

char* xstrncat(char* s1, char* s2, size_t len1, size_t len2)
{
	s1+=len1;
	while(len2--)
		*s1++=*s2++;
	return s1;
}

@Silverdream:
the problem in your function is the for-loop!
the index goes from 0 to n-1 and not form 0 to n

and why the hell you call the function xstrcmp?? it does not compare...

Thanx Shade. By the way i just misspelled strcat as strcmp.

Code:

char* xstrncat(char* s1, char* s2, size_t len1, size_t len2)
{
	s1+=len1;
	while(len2--)
		*s1++=*s2++;
	return s1;
}

This is good c but it lacks readability. Am I the only person here who thinks that code as above should read like this...

Code:

char* xstrncat(char* s1, char* s2, size_t len1, size_t len2)
{
	s1+=len1;
	while(len2)
        {
		*s1=*s2;
                 ++s1;
                 ++s2;
                 --len2;
        }
	return s1;
}

I think virtually any compiler will produce the same assembly language for this so why go with the former over the more readable latter.