Thread: Pointers Issue

Hello, I am attempting to write a program in which I write my own version of the library function 'strcat' using pointers:

Code:

#include "stdio.h"
#include "string.h"

void mystrcat(char *first, char *second);

int main(void)
{
    mystrcat("hello","world");
    getch();
    return 0;    
}
    
void mystrcat(char *first, char *second)
{
    char result[strlen(first)+strlen(second)];   
    
    while(*first) *result++ = *first++;
    while(*second) *result++ = *second++;
    *result = '\0';
    printf(result);
}

When I try to compile it, I get two errors saying "wrong type argument to increment". What is the problem?

Thanks, I made those edits to my code but I get exactly the same error when I try to compile it.

Well, result is not a pointer, it is an array. You can't increment an array. Either use a separate int variable for an index that gets incremented, or set up a legitimate pointer variable to increment.

Originally Posted by tabstop

Well, result is not a pointer, it is an array. You can't increment an array. Either use a separate int variable for an index that gets incremented, or set up a legitimate pointer variable to increment.

I thought you could use the name of an array without the index just like an ordinary pointer, but evidently this is not the case. I created another pointer like this

Code:

char *p;
p = result;

and used *p++ to increment it which compiles fine.

However I still get a garbage result when I run the program. I assume this is because of what you just said Maz, but I am a beginner at C and I don't really know what you are talking about when you refer to these stacks.

or just:

Code:

#include "stdio.h"
#include "string.h"

void mystrcat(char *first, char *second);

int main(void)
{
    
    mystrcat("hello","world");
    getch();
    return 0;    
}
    
void mystrcat(char *first, char *second)
{
    char result[strlen(first)+strlen(second)];   
    int i;
    for(i=0; i < strlen(first) + strlen(second); i++) {
    result[i] = 0;        
    }
    
    char *pointer1 = &result[0];
    char *pointer2 = &first[0];
    char *pointer3 = &second[0];
    while(*pointer2) {
         *(pointer1++) = *(pointer2++);
    }
    
    while(*pointer3) {
        *(pointer1++) = *(pointer3++);
    }
    *pointer1 = '\0';
    printf(result);
}

Thanks Drogin, but I have corrected my code and it now works as it should:

Code:

#include "stdio.h"
#include "string.h"

void mystrcat(char *first, char *second);

int main(void)
{
    mystrcat("hello"," world");
    getch();
    return 0;    
}
    
void mystrcat(char *first, char *second)
{
    char *p;
    char result[strlen(first)+strlen(second)];   
    
    p = result;
    
    while(*first) *p++ = *first++;
    while(*second) *p++ = *second++;
    *p = '\0';
    printf(result);
}

Ah, yeah, I see I overreacted about the pointers, lol