Yeah this is a simple question and pretty popular. And this is what I did.
There is a segmentation fault when we copy characters from src into dest . Now, I can understand the source of this fault - when we iterate over the dest string we reach the end and then the dest pointer points to the 'string terminator' or 0. So next when we put *dest++=*src++ it obviously will give an error.

//includes
void concat(char * dest, const char * src) {    
      while (*dest) ++dest;    
      while (*dest++ = *src++);     
 }

void main(){
	concat("hi","hello");
	getch();
}

The only way to beat this is to preallocate memory equal to the sum of both the strings - but that kind of beats the purpose of this method. And secondly I have searched online and found similar codes.

What am I missing?

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my bad. it seems even the inbuilt strcat fails and the simple reason is not enough space in the destination string.
one way to get past this is to declare a long string array and have a char pointer point to it. you can send this pointer to strcat as the first pointer.

but still i am not satisfied-there must be some other alternative!

Yeah this is a simple question and pretty popular. And this is what I did.
There is a segmentation fault when we copy characters from src into dest . Now, I can understand the source of this fault - when we iterate over the dest string we reach the end and then the dest pointer points to the 'string terminator' or 0. So next when we put *dest++=*src++ it obviously will give an error.

//includes
void concat(char * dest, const char * src) {    
      while (*dest) ++dest;    
      while (*dest++ = *src++);     
 }

void main(){
	concat("hi","hello");
	getch();
}

The only way to beat this is to preallocate memory equal to the sum of both the strings - but that kind of beats the purpose of this method. And secondly I have searched online and found similar codes.

What am I missing?

You can't concantinate one string literal to another string literal because both string literals are normally (but not always) placed in read-only memory. What you have to do is below. Your concat() function should work ok as you wrote it.

int main()
{
   char s1[255] = "Hello ";
   concat(s1,"World");
}

>>there must be some other alternative!
There is -- see strcat_s(), but that is not a standard C function.

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