Simple Encryption Program

This is a discussion on Simple Encryption Program within the C Programming forums, part of the General Programming Boards category; First off let me say that I appreciate any help that I recieve. Okay, here is my problem: I am ...

  1. #1
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    Simple Encryption Program

    First off let me say that I appreciate any help that I recieve.

    Okay, here is my problem:

    I am writing a simple encryption program that will encrypt text files. The encryption key to decrypt the files is held at the very beginning and is seperated by a tab from the rest of the files.

    Example:

    2344321[tab]afldsfjkasldfkjasljkfsajfal;kf;lkkl;adfkl;a.

    My question is how would I go about reading the first few numbers from the tab and then continue to read the other characters. I am using rand to generate the key and I seeded it with the time.

    My main problem is taking in the numbers on as a whole integer instead of passing them into an array. How would I go about doing this and still be able to scan the rest of the file.

    I appreciate any assistance.

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    To me it sounds like you'd first want to use something like fscanf with a %d to obtain the key. Then you'd skip the tab and encrypt the rest of the characters obtained with something like fgetc.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    cwr
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    Just use atoi or strtol or sscanf to read the number from your char array into an int.

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    Okay.. .but how do I tell the compiler to scan everything up the the tab? I pretty much got it after that I think.

    Hm..... I would think this would work but it doesn't"
    Code:
    while ((x=fgetc(fpdata) ! = '\t'))
             {
                key[i] = x;
                i++
             }
    Then after it reaches the tab it goes ahead and scans the rest of the document with fget c

    Code:
    tab = fgetc(fpdata);
    while  ( ( x = fgetc( fpAtad ) ) != EOF )
                {
                    printf( "%c", x );
                }

  5. #5
    Just Lurking Dave_Sinkula's Avatar
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    Like I said earlier.
    Code:
    #include <stdio.h>
    
    int main(void )
    {
       static const char filename[] = "file.txt";
       FILE *file = fopen(filename, "r");
       if ( file )
       {
          int key;
          char tab;
          if ( fscanf(file, "%d%c", &key, &tab) == 2 && tab == '\t' )
          {
             printf("key = %d\n", key);
             for ( ;; )
             {
                int c = fgetc(file);
                if ( c == EOF )
                {
                   break;
                }
                /* do stuff (here I'll just print the character) */
                putchar(c);
             }
          }
          fclose(file);
       }
       else
       {
          perror(filename);
       }
       return 0;
    }
    
    /* my output
    key = 2344321
    afldsfjkasldfkjasljkfsajfal;kf;lkkl;adfkl;a.
    */
    Although you may want to open the file in binary mode.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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