pointer c string

[sdsu619]

Hey I am trying to work on a problem:
----------------------------------------------------------------------------
Write a function named removeS that accepts one character pointer as a parameter and returns no value. The parameter is a C string. This function must remove all of the upper and lower case 's' letters from the string. The resulting string must be a valid C string.

Your function must declare no more than one local variable in addition to the parameter; that additional variable must be of a pointer type. Your function must not use any square brackets and must not use the strcpy library function.

int main()
{
char msg[50] = "She'll be a massless princess.";
removeS(msg);
cout << msg; // prints he'll be a male prince.
}

---------------------------------------------------------------------------
Since I'm only allowed to make one local variable of a pointer, I'm guessing making a new c string is out of the question. I made a for loop that checks for an 's' and replaces it with the next letter.

void removeS(char* message)
{
	char* ptr = message;
	for(; *ptr != '\0'; ptr++)
	{
		while(*ptr == 's' || *ptr == 'S')
		{
			*ptr = *(ptr+1);
			
		}
	}
}

Is this the right way to go about the problem? If so, how can I solve the problem of the rest of the characters?(She'll would become hhe'll)?
Or is there another more straightforward way of doing it

[Cubbi]

Nice input string.

Your hint is helpful: the simple way to go about it is to create another pointer, and run through the string with two pointers. One (the original function parameter) stepping through every character. The other (the new one) also stepping through every character, but skipping any 's' or 'S'. The loop would copy the character from the second pointer to the first:

void removeS(char* message)
{
    for(char* p = message; *p; )
    {
        while(*p == 's' || *p == 'S')
            ++p;
        *message++ = *p++;
    }
    *message = '\0';
}

[sdsu619]

Ah good idea thanks!
in the for loop, what is the purpose of the condition statement *p? Isn't it not checking for anything?

[Cubbi]

it's shorthand for *p != '\0' in this case

[sdsu619]

oh ok, sorry is
*message++ = *p++;

also shorthand for

*message = *p
message++;
p++;

?

[Cubbi]

Yes, *p++ = *q++ is also a very common C idiom, I think it is more recognizable than something like

for(char* p = message; *p != '\0'; ++p, ++message)
{
     while(*p == 's' || *p == 'S')
         ++p;
     *message = *p;
}

(although this is probably a better-looking use of a for-loop).

[vlad from moscow]

My five cents

void remove( char *s )
{
	char *p = s;

	do
	{
		if ( *s != 's' && *s != 'S' ) *p++ = *s;
	} while ( *s++ );
}