Thread: Urgent-Need help with this problem

rite a program that will create scrambled words by
circularly rotating the middle characters of each word by 1 character. Place
the scrambled words, 1 per line in an output file.
Example:
hamster ---> hmstear
The Input File format is such that the first line
contains a number indicating the number of words in the file, followed by one
line for every word to be scrambled (no spaces in any of the words).

Sample input file:
4
dog
pepper
marker
teapot
Sample output file:

dog
pppeer
mrkear
tapoet

No word is more than 80 characters long in the
input file.

The input file name is dict.txt . Put all
output in a file called scramble.txt

If a file fails to open, ensure you display an
appropriate error message.

If the first line of the input file does not
contain a number, display an error message and stop.

-------------------------------------------------------------------------------------
Here is what I have so far:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
 
int main(void) { 
 FILE *ifp, *ofp;
 char *mode = "r";
 char inputFilename[] = "dict.txt";
 char outputFilename [] = "scramble.txt";
 int flag, status;
 int num = 0;
 char words[4][20];
 int i,j,len,idx;
 char c;
 ifp = fopen(inputFilename, mode);
 if(ifp == NULL)
 {
  flag=1;
  printf("Error-Can't open the input file dict.txt!\n");
  return 1;
 }
 status = fscanf(ifp, "%d", &num);
 if(status !=1)
 {
  printf("Error-The first line of the file does not contain a number\n");
  return 1;
 }
 i=0;
 while (!feof(ifp)){
  fscanf(ifp, "%s", words[i]);
  i++;
 }
 for(i=0;i<num;i++) {
      len=strlen(words[i])-2;
      for(j=1;j<len;j++) {
         idx = j;
         while(idx==j)
           idx=rand() % len+1; 
   
  
          
         //swap
         c=words[i][j];
         words[i][j] = words[i][idx];
         words[i][idx] = c;      
         
      }
 }
   for(i=0;i<num;i++)
      printf("%s\n",words[i]);
 
  
   return 0;
}

in the output it only moves three of the characters and for some reason I cannot get all four to move. Also I need the 2d array to match the integer in the fist line of the file. I am not to familiar with dynamic memory allocation and could not get it to work....
Can some one point me in the right direction. any help would be appreciated

Originally Posted by 1rmohebian

I tried using an array of 80 chars but I end up with an exception error.

Use an array of 81 characters: 1 for the null character.

Originally Posted by 1rmohebian

Any ideas on how to tackle the problem?

Instead of dumping everything into a single main function, I would write a function that takes a char* that points to the first element of an array of char, and which will then scramble the string stored in that array. I would write the main function to test it. When I am sure that it works, I will then rewrite the main function to read input line by line from the file and call this function in the process of writing the output to another file. Since this is done line by line, only a single array is needed.

You need to read this
A development process

Then you need to break the problem down into a series of smaller steps. Mad bashing of the keyboard to produce a whole program, then wondering why it doesn't work isn't how to go about it.

Say for example

Code:

int main ( ) {
  char test[] = "ThisIsATest";
  printf("Scramble=%s\n", scramble(test) );
}

There isn't a lot of point in messing about with file handling until this part works.
And don't just stop when the first test passes, try other examples as well.

Similarly, make sure you know how to read a file, by just printing the words

Code:

while (!feof(fpin)){
    fscanf(fpin, "%s", word);
    printf("Read word=%s\n", word );
}

Again, make sure it works (FYI, it doesn't, but that's for you to find out).

Why is your scrambling random? I thought it was supposed to be by rotating one character

For starters, you need to indent your code properly, e.g.,

Code:

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

char *scramble(char *str);

int main()
{
    char word[81];
    FILE *fpin;
    FILE *fpout;
    int status, num;

    /* open the input file -- quit if not found */
    fpin = fopen("dict.txt", "r");
    if (fpin == NULL)
    {
        printf("Error-Can't open the input file dict.txt!\n");
        printf("Press the enter key to end program!");
        getchar();
        return 1;
    }

    /* Check to ensure that the first line of the file contains a number -- quit if not found */
    status = fscanf(fpin, "%d", &num);
    if (status != 1)
    {
        printf("Error-The first line of the file does not contain a number\n");
        printf("Press the enter key to end program!");
        getchar();
        return 1;
    }

    /* open the output file */
    fpout = fopen("scramble.txt", "w");

    /* read one line at a time and send to scramble function and print out */
    while (!feof(fpin))
    {
        fscanf(fpin, "%s", word);
        fprintf(fpout, "%s\n", scramble(word));
    }

    return 0;
}

/* Scramble function receives a pointer to the array of words and returns a pointer to the same array*/
char *scramble(char *str)
{
    int j, len;
    char c;
    len = strlen(str) - 2;

    //finds the length of word excluding the first and last character
    for (j = 1; j < len; j++)
    {
        //swap
        c = str[j];
        str[j] = str[j + 1];
        str[j + 1] = c;
    }

    return str;
}

If you want to use tabs for indentation then take care to use only one tab per indent level. Otherwise, choose a consistent number of spaces (between 2 to 8; I personally prefer 4) per indent level.

It is not correct to use feof to control a loop in the way that you did. It is also not correct to use "%s" as the format string to read a string, because it does not account for the fact that the destination array is finite. Rather, you should write something like:

Code:

while (fscanf(fpin, "%80s", word) == 1)
{
    fprintf(fpout, "%s\n", scramble(word));
}

Remember to close the files after you are done with them: this is a good habit. This should also happen for the input file when you end because of invalid input, although if I remember correctly the file will be closed anyway when the program terminates.

Originally Posted by 1rmohebian

The problem seems to be in my scramble function. it is not scrambling based on the requirements. I have tried everything and like I mentioned it works for the words provided in my description above but not for words that have more then 6 chars.....

I tried with "teapots" and got "tapotes", which looks correct to me. "hamster" resulted in "hmstear", which is the example that you quoted.

Without a reference to your current code? Not as well as it would (unless it has not changed from your last post.)