why/where to point in C program

chens_83 · 01-29-2003, 07:56 AM

ok i understand this program up until the point where i need to have a guard for a do-while

Code:

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

int main (void)
{
char str[80];
FILE *fp;   

fp = fopen("TEST.txt","w"); 
							
	if(fp==NULL)
	{
		printf("CAnnot open file.\n"); 
		exit(1);
	}

	do
	{
		printf("Enter a String (Enter to quit) : ");
		gets(str);
		strcat(str,"\n"); 
		fputs(str,fp); 
	}while(*str != '\n');  //why dereference?

return 0;
}

I am confused to why i need to point at the while's guard?
can some one please push me in the right direction, or explain why.

-Chensy in a frenzy

moeminhtun · 01-29-2003, 10:10 AM

*str is the reference to the first element of the array "str" which is str[0].
If a user didn't enter anything and just press enter, the str[0] would be '\n' and the program will exit.
So the purpose is to exit the program when the user press "Enter".
*str != '\n' is the same as str[0] != '\n'

GtkUser · 01-29-2003, 11:17 AM

You can condense it like this:

Code:

#include<stdio.h>

int main()
{
  FILE *fptr = NULL;
  char buff[255];

  fptr = fopen("myfile","w");

  do
    {
      fgets(buff, 255, stdin);
      fputs(buff, fptr);
    }while (*buff != '\n');


  fclose(fptr);
  return 0;
}

chens_83 · 01-29-2003, 05:47 PM

Ok . Thanks for the help. Ok that reference was a little confusing, i would of just used str[0]. Is the pointer way that much quicker instead of using the str[0] ?

GtkUser · 01-29-2003, 07:28 PM

The array decays into a pointer. It's not going to make a difference in speed though.

llama_meme · 01-30-2003, 01:50 PM

It's useful to know that:

Code:

array[x]

is just syntactic sugar for:

Code:

*(array + x)

In the case of your program, x was 0, so *(array + x) went to *array.

Alex