Strings and arrays in C

crystalattice · #1 18-Apr-2004, 14:21

Task: write an interactive program the reads in 7 strings using scanf(), print them as a list, then sort them alphabetically and print a new list.

I am thinking of using an array to store the strings but it doesn't seem to be working. I think it requires a 2d array because I want to store multiple words, but even when I test it w/ just a single array, I don't get an output.

Here's my test code:

CPP / C++ / C Code:

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

#define N_STRINGS 7

int main()
{
	
	const char array[N_STRINGS] = {0};
	int i;
	
	printf("Please enter 7 strings.\n");
	for (i=0; array[i]<N_STRINGS; ++i)
		scanf("%s", array);
	for (i=0; array[i]<N_STRINGS; ++i)
		printf("%s", array);
	return 0;
}

When run, this code will accept an input, but doesn't print an output. In my debugger, when I step through I can see a single string being written to the array but all array indexes after the word are nulled out, e.g. type in "one" and "two" and the array is written as :

array[0]='o'
array[1]='n'
array[2]='e'
array[3] through array[6]='\0'

Now, when the printf() is run, nothing is printed, even though there is something in the array.

I've tried moving the i counter from the for loop to the body, as in scanf("%s", array[i]) and the for loop to just "i < N_STRINGS" but that doesn't help.

Unfortunantly, my textbooks don't give similar examples to this and I can't find anything specific on the 'net. About the only thing I've found is that scanf() can be used to input a string to an 1d array and printf() will print this array. I've tested this seperately so I know this works, but I can't seem to get it to work w/ this problem.

Hope I don't sound like a clueless noob.

Any thoughts?

dsmith · #2 18-Apr-2004, 14:48

Hi Crystalattice. You do need a 2d array. When you define:

CPP / C++ / C Code:

	
	const char array[N_STRINGS] = {0};

You are simply getting an array of characters which is one string. In this case, it is being initialized with Nulls, so every position will be filled with 0 (Null).

I ran your code and got exactly what I would expect. A single input prompt and the printout of what I input. Perhaps, adding a newline will help you see your output, such as:

CPP / C++ / C Code:

		printf("\n%s\n", array);

Beyond that your code needs to be changed to use either a ragged array or a 2d char array.

HTH,
d

crystalattice · #3 27-Apr-2004, 17:30

So, I realize that I need a 2d array, but how do I fill it using scanf()? My books don't cover it very well; they mostly talk about getchar(). Can I use a loop to fill it like if I used getchar()? I tried it both w/ a for loop and while loop but it didn't work. I would think you could use '\0' for the loop-stop condition, since it's the last entry in an array, but it doesn't work.

How else can you fill an array w/ scanf()?

Thanks for the help.

Max Payne · #4 27-Apr-2004, 19:53

First,Your for loop doesn't seem quite right.

for (i=0; array[i]<N_STRINGS; ++i)

the condition array[i]<N_STRINGS should be change to i<N_STRINGS,

You need to clear terminating newline ('\n' or ENTER ) from the input stream before calling scanf() again.
So to clear the buffer use the fflush(stdin); // in c
or
cin.clear(); //clears the buffer
cin.sync(); // syncronize it

so, with all the changes, here is the new code.

CPP / C++ / C Code:

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

#define N_STRINGS 7

int main()
{
  char array[N_STRINGS][10];

  int i;
  printf("Please enter 7 strings.\n");
  for (i=0; i<N_STRINGS; ++i)
  {
    scanf("%s",array[i]);
	fflush(stdin);
  }
  for (i=0; i<N_STRINGS; ++i)
    printf("%s\n",array[i]);
  return 0;
}

WaltP · #5 28-Apr-2004, 00:28

Quote:

Originally Posted by Max Payne

So to clear the buffer use the fflush(stdin); // in c

No you don't. The standard states that fflush() is not defined for input streams. It may or may not work -- different compilers do different things. Stay away from fflush(stdin);

CPP / C++ / C Code:

scanf("%s",array[i]);

is also dangerous. Execute this program:

CPP / C++ / C Code:

#include <stdio.h>
int main()
{
    char tmp[8];
    scanf("%s", tmp);
    printf("%s\n", tmp);
    return 0;
}

and enter 20 characters for tmp. You are able to easily overwrite memory. My test crashed! So since you are simpy entering a character string, a much safer way is to use fgets:

CPP / C++ / C Code:

rc = fgets(array[i], 10, stdin);

crystalattice · #6 11-May-2004, 19:01

Just wanted to say thanks for the help. My program works now, thanks to everyone. As a matter of fact, I'm still waiting for my school to get back to me about how to work this problem, so this forum is way better when I need help.

Thanks again.

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Strings and arrays in C

Still have problems

Sorry 'bout the wait