Question

I was trying to concatenate 2 strings without using strcat, but I am getting a runtime error. Please, someone help me out here…

Also, is this statement q=q+len; correct? Can we add a variable to a pointer??

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

void xstrcat(char*,char*);
int main()
{
    char source[]="folks";
    char target[30]="hello";
    xstrcat(target,source);
    printf("%s",source);
    printf("%s",target);
    return 0;
}

void xstrcat(char*p,char*q)
{
    int len=0;
    len=strlen(q);
    q=q+len;
    while(*p!='\0')
    {
        *q=*p;
        q++;
        p++;
    }
    *q='\0';
}

Answer 1

Some mistakes in your implementation:

1 – You are accessing random memory. Once you don’t have a /0 in your string.

while(*p!='/0')

must be:

while(*p!='\0')

Note the slash \.

2 – You are overwriting random memory when try to add *p into *q. You must create a new variable with enough space for store them.

Also, is this statement q=q+len; correct? Can we add a variable to a
pointer??

Yes. It’s a pointer arithmetic expression.