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Nov 27th, 2006

Copying words into an array of char ?!?

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Hello ladies and gents,

I'm trying to copy two words, for instance test and word into an array of characters and have this:

C Syntax (Toggle Plain Text)
#include <iostream>
 
int main()
{
	char word[10]= "";
	char *wordArr[10];
 
	for(size_t i = 0; i < 2; i++)
	{
		std::cin >> word;
		*(wordArr + i)  = word;
	}
 
	for(size_t i = 0; i < 2; i++)
		std::cout << wordArr[i] << '\n';
 
	std::cin.ignore(2);
 
	return 0;
}
#include <iostream>

int main()
{
	char word[10]= "";
	char *wordArr[10];

	for(size_t i = 0; i < 2; i++)
	{
		std::cin >> word;
		*(wordArr + i)  = word;
	}

	for(size_t i = 0; i < 2; i++)
		std::cout << wordArr[i] << '\n';

	std::cin.ignore(2);
	
	return 0;
}

Thing is, it prints the last word twice as if it doesn't store the first word, what am I doing wrong, can anyone point me in the right direction?

I know I could use strings or even a vector, but, my idea is to work out a version using characters first, then strings and then a vector.

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JoBe

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Nov 27th, 2006

Re: Copying words into an array of char ?!?

Well, found a solution like this:

C Syntax (Toggle Plain Text)
#include <iostream>
 
int main()
{
	char word[10]= "";
	char wordArr[10][10];
 
	for(size_t i = 0; i < 2; i++)
	{
		size_t j;
		std::cin >> word;
		for(j = 0; j < strlen(word); j++)
			wordArr[i][j] = word[j];
		wordArr[i][j] = '\0';
	}
 
	for(size_t i = 0; i < 2; i++)
	{
		for(size_t j = 0; j < strlen(wordArr[i]); j++)
			std::cout << wordArr[i][j];
		std::cout << '\n';
	}
 
	std::cin.ignore(2);
 
	return 0;
}
#include <iostream>

int main()
{
	char word[10]= "";
	char wordArr[10][10];

	for(size_t i = 0; i < 2; i++)
	{
		size_t j;
		std::cin >> word;
		for(j = 0; j < strlen(word); j++)
			wordArr[i][j] = word[j];
		wordArr[i][j] = '\0';
	}

	for(size_t i = 0; i < 2; i++)
	{
		for(size_t j = 0; j < strlen(wordArr[i]); j++)
			std::cout << wordArr[i][j];
		std::cout << '\n';
	}

	std::cin.ignore(2);
	
	return 0;
}

But, there has to be a way of using

char *wordArr[10];

right?

It would make it easier since the use of a pointer to an array of char's wouldn't need to be terminated by yourself, the compiler would do this like Ancient Dragon said in another thread right.

Does any of you guys know how I could use that type of definition in my program?

JoBe

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Nov 27th, 2006

Re: Copying words into an array of char ?!?

Hope something in here meets your needs and helps you understand the syntax.

char * wordArr[10];

means wordArr is an array of 10 char pointers, not that wordArray is a pointer to 10 char arrays.

char * word = new char[10];

means word is a pointer to a char array that can contain up to 10 char.

Now, an example of putting words into array directly. without need for user termination

C Syntax (Toggle Plain Text)
#include <iostream>
using namespace std;
 
int main()
{
   char word[10]= "";
   char wordArr[10][10];
   int i;
 
   for(i = 0; i < 10; ++i)
       cin >> wordArr[i];
 
   for(i = 0; i < 10; ++i)
       cout << wordArr[i] << endl;
 
   cin.get();
}
#include <iostream>
using namespace std;

int main()
{
   char word[10]= "";
   char wordArr[10][10];
   int i;

   for(i = 0; i < 10; ++i)
       cin >> wordArr[i];
  
   for(i = 0; i < 10; ++i)
       cout << wordArr[i] << endl;
   
   cin.get();
}

Inputting words into an array indirectly

C Syntax (Toggle Plain Text)
#include <iostream>
using namespace std;
 
int main()
{
    char word[10] = "";
    char wordArr[10][10];
    int i;
 
    for(i = 0; i < 10; ++i)
    {
        cin >> word;
        strcpy(wordArr[i], word);
    }
 
    for(i = 0; i < 10; ++i)
        cout << wordArr[i] << endl;
 
    cin.get();
}
#include <iostream>
using namespace std;

int main()
{
    char word[10] = "";
    char wordArr[10][10];
    int i;

    for(i = 0; i < 10; ++i)
    {
        cin >> word;
        strcpy(wordArr[i], word);
    }

    for(i = 0; i < 10; ++i)
        cout << wordArr[i] << endl;

    cin.get();
}

Using pointer to pointer to char instead of array of char arrays

C Syntax (Toggle Plain Text)
#include <iostream>
using namespace std;
 
int main()
{
   char  **wordArr;
   int i, j, k;
   cin >> i;
   cin >> j;
   wordArr = new char*[i];
   for( j = 0; j < i; ++i)
     wordArr[i] = new char[j];
 
   for(j = 0; j < i; ++j)
      cin >> wordArr[j];
 
   for(j = 0; j < i; ++j)
      cout >> wordArr[j] << endl;
 
   for(j = 0; j < i; ++j)
      delete[] wordArr[i];
 
   delete wordArr;
    cin.get();
}
#include <iostream>
using namespace std;

int main()
{
   char  **wordArr;
   int i, j, k;
   cin >> i;
   cin >> j;
   wordArr = new char*[i];
   for( j = 0; j < i; ++i)
     wordArr[i] = new char[j];
   
   for(j = 0; j < i; ++j)
      cin >> wordArr[j];

   for(j = 0; j < i; ++j)
      cout >> wordArr[j] << endl;
   
   for(j = 0; j < i; ++j)
      delete[] wordArr[i];
  
   delete wordArr;
    cin.get();
}

Using array of char pointers instead of pointer to pointer to char

C Syntax (Toggle Plain Text)
#include<iostream>
using namespace std;
 
int main()
{
   char *wordArr[10];
   int i, j;
   cin >> j;
 
   for(i = 0; i < 10; ++i)
      wordArr[i] = new char[j];
 
   for(i = 0; i < 10; ++i)
      cin >> wordArr[i];
 
   for (i = 0; i < 10; ++i)
      cout << wordArr[i] << endl;
 
   for(i = 0; i < 10; ++i)
       delete[] wordArr[i];
 
   cin.get()
}
#include<iostream>
using namespace std;

int main()
{
   char *wordArr[10];
   int i, j;
   cin >> j;

   for(i = 0; i < 10; ++i)
      wordArr[i] = new char[j];
   
   for(i = 0; i < 10; ++i)
      cin >> wordArr[i];

   for (i = 0; i < 10; ++i)
      cout << wordArr[i] << endl;

   for(i = 0; i < 10; ++i)
       delete[] wordArr[i];
   
   cin.get()
}

Another version using array of char pointers:

C Syntax (Toggle Plain Text)
#include <iostream>
using namespace std;
 
int main()
{
   char * wordArr[2] = { {"Hello"}, {"World"} };
   cout << wordArr[0] << ' ' << wordArr[1] << endl;
 
   cin.get()
}
#include <iostream>
using namespace std;

int main()
{
   char * wordArr[2] = { {"Hello"}, {"World"} };
   cout << wordArr[0] << ' ' << wordArr[1] << endl;

   cin.get()
}

Last edited by Lerner; Nov 27th, 2006 at 11:00 am.

Lerner

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Nov 27th, 2006

Re: Copying words into an array of char ?!?

Thanks for those examples Lerner. The reason I came up with my first example code was because the exercise tells you not to store two identical words, therefore I used two variables char word[10]= ""; and char wordArr[10][10];. That way, I can compare when entering a new word with the already added words to check whether it's not in the list.

I should've written the exercise out, but, I wanted to take this one in small parts as you guys always tell forumers to do, so they don't get overwhelmed with the code. Sorry for that. Anyway, the exercise goes as follows:

- Read a sequence of words from input. Use Quit as a word that therminates input. Print the words in the order they were entered. Don't print a word twice. Modify the program to sort the words before printing them.

I'll be back next week-end, don't have the time to do the exercise now, anyway, thanks again for the thourough explanatioin and examples :!:

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

Hey Lerner,

Finally got time to work on this exercise again, but, before I do, I'd like to ask whether this way of adding a word into another array is good or not. If not, what are the reasons this is not ideal?

C Syntax (Toggle Plain Text)
for(size_t i = 0; i < 2; i++)
	{
		size_t j;
		std::cin >> word;
		for(j = 0; j < strlen(word); j++)
			wordArr[i][j] = word[j];
		wordArr[i][j] = '\0';
	}
for(size_t i = 0; i < 2; i++)
	{
		size_t j;
		std::cin >> word;
		for(j = 0; j < strlen(word); j++)
			wordArr[i][j] = word[j];
		wordArr[i][j] = '\0';
	}

The intention here was just two add two words into the array to try out. Was I correct that I had to add the '\0'to the end of the word so that it would be correctly terminated?

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

Hi guys,

Was wondering if any of you could help me out, I'm trying to print the words only once, but, it seems I'm doing something wrong, could someone point me in the right direction?

C Syntax (Toggle Plain Text)
#include <iostream>
#include <cstring>
 
int main()
{
	char wordArr[5][10];
	short contr;
 
	for(size_t i = 0; i < 5; i++)
		std::cin >> wordArr[i];
 
	for(size_t i = 0; i < 5; i++)
	{
			contr = strcmp(wordArr[i], wordArr[i+1]);
 
			if (contr != 0)
				std::cout << wordArr[i] << '\n';
	}
 
	std::cin.ignore(2);
 
	return 0;
}
#include <iostream>
#include <cstring>

int main()
{
	char wordArr[5][10];
	short contr;

	for(size_t i = 0; i < 5; i++)
		std::cin >> wordArr[i];

	for(size_t i = 0; i < 5; i++)
	{
			contr = strcmp(wordArr[i], wordArr[i+1]);
			
			if (contr != 0)
				std::cout << wordArr[i] << '\n';
	}

	std::cin.ignore(2);
	
	return 0;
}

JoBe

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

Why ain't you using std::strings?

iamthwee

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

Just wanted to tell you that sometimes your description is rather vague. Always post a question in such way that the person reading it doesn't have to use a compiler to test it out what is going wrong.

If your program displays something and takes some kind of user input, just paste a sample output which is erroneous or not as expected along with what did you expect. This kind of description will help us understanding the problem better.

Now as per your question is concerned, your program only checks to see whether the preceding string is equal to the current string and if it is so then it just skips printing the current string. But your program will fail in conditions where you alternate the words inputted to the program like:

hello
hell
hello
hell
hello

I hope you understand the twist .

~s.o.s~

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

>>Was I correct that I had to add the '\0'to the end of the word so that it would be correctly terminated?

No, cin >> automatically null terminates input from either the keyboard or antother stream. The same goes for getline(), which is another way to read in a string.

C Syntax (Toggle Plain Text)
for(size_t i = 0; i < 5; i++) //for each word in the array
{
   //compare this word with the next word in the array
   contr = strcmp(wordArr[i], wordArr[i+1]);
 
     //if the two words are not the same
     if (contr != 0)
        //print out current word
        std::cout << wordArr[i] << '\n';
}
for(size_t i = 0; i < 5; i++) //for each word in the array
{
   //compare this word with the next word in the array
   contr = strcmp(wordArr[i], wordArr[i+1]);

     //if the two words are not the same
     if (contr != 0)
        //print out current word
        std::cout << wordArr[i] << '\n';
}

You don't want that for two reasons. Number one, when i == 4 you will try to compare wordArr[4] with wordArr[5] but wordArr[5] doesn't exist. If you are lucky your program will crash. If you are unlucky you will get undefined behavior and who knows what will happen, it may even appear to work correctly. Number two, the logic isn't what you want. You want:

C Syntax (Toggle Plain Text)
bool found = false
for each word in the array //this word
   for each word prior to this word //current word
      if this word is the same as current word
         set found to true
   if not found 
      print out this word
bool found = false
for each word in the array //this word
   for each word prior to this word //current word
      if this word is the same as current word
         set found to true
   if not found 
      print out this word

Lerner

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Dec 2nd, 2006

Re: Copying words into an array of char ?!?

Click to Expand / Collapse Quote originally posted by iamthwee ...

Why ain't you using std::strings?

>> First post "I know I could use strings or even a vector, but, my idea is to work out a version using characters first, then strings and then a vector."

Quote originally posted by ~s.o.s~ ...

Just wanted to tell you that sometimes your description is rather vague. Always post a question in such way that the person reading it doesn't have to use a compiler to test it out what is going wrong.

I'll try my best to explain it more thoroughly next time :!:

@ Lerner, thanks for the explanation.

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