Thread: Unable to pinpoint my mistake for a seemingly simple K&R exercise.

I am trying to work on a problem mentioned in K&R book (Excercise 2-4).

Exercise 2-4. Write an alternative version of squeeze(s1,s2) that deletes each character in s1 that matches any character in the string s2.

I am not writing a separate function, I am trying to achieve squeeze(s1,s2) by writing the code in the main program itself. Here is the code:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
const char msg[15] = "blueberry";
int c;
int s[15];
int j = 0;
int i = 0;
int k= 0;
int ok = 0;


for (i = j = 0; i<=15 && (c = getchar()) != '\0'; ++i)
{
	s[i] = c;
	ok = 1;
for (k=0; k <= 15; ++k)
{
	if (s[i] == msg[k]){
	ok = 0;
	}
}
if (ok == 1)
{
	s[j] = s[i];
	j++;
}
}
s[j] = '\0';

for (j = 0; j<= 15; ++j)
	printf ("%c ", s[j]);
}

Keyboard input:

blackberry

Desired output:

u

My output:

l a c k b e r r y

I've done several dry-runs but I cannot figure out where I am going wrong!? Why is control entering highlighted loop even if the condition is false? Extremely baffled! Please help.

The reason control enters the inner loop always is because the inner loop has to be executed before the outer loop has its next iteration. Imagine if I counted to ten three times.

Code:

for ( i = 0; i < 3; i++ ) {
   for ( cnt = 1; cnt <= 10; cnt++ ) {
      printf( "%d ", cnt ); 
   }
   printf( "\n" );
}

Just about the only way to do it, right? It works the same way no matter what the actual purpose is.

You should probably get all of the input before you start to squeeze() it. Also be careful with arrays -- an arrays size is not a valid subscript.

I changed:

Code:

for (t=j=0; s[t] != '/0'; ++t)
{
       ok = 1;
for (k=0; msg[k] != '/0'; ++k)

to:

Code:

for (t=j=0; s[t] != '\0'; ++t)
{
       ok = 1;
for (k=0; msg[k] != '\0'; ++k)

and got it to compile. Not sure what you're supposed to do with it when you run it, but I figure you can go from there.

Thanks for the help everyone. I have managed to get some output from the program. It helped me clear some concepts.

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
const char msg[15] = "blueberry";
int c;
char s[15];

int j = 0;
int i = 0;
int nomatch = 0;
while (i < 15 && (c = getchar()) != '\n')
{
	s[i] = (char) c;
	++i;
}
s[i] = '\0';
printf("input: %s\n", s);
printf ("value of i %d",i);
printf("\nmessg: %s\n", msg);

for (i=j=0; s[i] != '\0'|| msg[i] != '\0';)
{
	nomatch = 0;

	if (s[i] != msg[i])
		{
			nomatch = 1;
	}

	if (nomatch == 1)
	{
		s[j] = s[i];
		         j++;
}

	++i;
}
s[j] = '\0';
printf ("output: %s		", s);
}