Ceasar Shift program

This is a discussion on Ceasar Shift program within the C Programming forums, part of the General Programming Boards category; Hey there guys, I am currently in the process of writing a ceasar shift program for UNI and would really ...

  1. #1
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    Ceasar Shift program

    Hey there guys,

    I am currently in the process of writing a ceasar shift program for UNI and would really appreciate some advice. I have pretty much finished the program but there are 2 elements that are stumping me at the moment.
    Basically the help I need is on the function below:

    Code:
    void decryptEncryptLine(int shift) {
      char input;
      char output;
      const char SENT = '\n';
      
      printf("Please enter characters to be encrypted/decrypted\n\n");
      scanf("%c", &input);
                
      while (input != SENT){ // while input is a character
    
              input = (toupper(input)); // convert lowercase to uppercase
              output = input + (shift); // apply ceasar shift
              
              
              if (output > 90) { // encode wrap around
                         output -= 26;
                         }
              
              else if (output < 65) { // decode wrap around
                      output += 26;
                      }
                      
              
              printf("%c",output);
              scanf("%c", &input);
             
              }
              
    }
    the above function takes one input character at a time and applies the ceasar shift then once a "\n" is detected the loop terminates then prints out the shifted characters. The problem I am having is that when it encounters a space, the program shifts the space and I dont want it to. Instead of a space I get the shifted ASCII character. Im not really sure how to go about enabling the user to enter a space and then just print the space with no shift. The other problem that i am having is that I need to use the isalpha() function so that the function will only accept alpha characters. I am also having trouble implementing this. I have tried various ways to incorporate these elements but the out put is never what I want it to be. so far the output looks like this:

    i like to eat pizza
    N?QNPJ?YT?JFY?UNEEF

    Which is correct for the shift but if i try to include these 2 elements the output changes and I end up with everything being displayed up to the first space, then nothing after that. So basically this is as good as I can get it at this stage.

    Any help/advice would be hugely appreciated.

    Thanks Guys

  2. #2
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    Quote Originally Posted by trevordunstan View Post
    Hey there guys,

    I am currently in the process of writing a ceasar shift program for UNI and would really appreciate some advice. I have pretty much finished the program but there are 2 elements that are stumping me at the moment.
    Basically the help I need is on the function below:

    Code:
    void decryptEncryptLine(int shift) {
      char input;
      char output;
      const char SENT = '\n';
      
      printf("Please enter characters to be encrypted/decrypted\n\n");
      scanf("%c", &input);
                
      while (input != SENT){ // while input is a character
    
              input = (toupper(input)); // convert lowercase to uppercase
              output = input + (shift); // apply ceasar shift
              
              
              if (output > 90) { // encode wrap around
                         output -= 26;
                         }
              
              else if (output < 65) { // decode wrap around
                      output += 26;
                      }
                      
              
              printf("%c",output);
              scanf("%c", &input);
             
              }
              
    }
    the above function takes one input character at a time and applies the ceasar shift then once a "\n" is detected the loop terminates then prints out the shifted characters. The problem I am having is that when it encounters a space, the program shifts the space and I dont want it to. Instead of a space I get the shifted ASCII character. Im not really sure how to go about enabling the user to enter a space and then just print the space with no shift. The other problem that i am having is that I need to use the isalpha() function so that the function will only accept alpha characters. I am also having trouble implementing this. I have tried various ways to incorporate these elements but the out put is never what I want it to be. so far the output looks like this:

    i like to eat pizza
    N?QNPJ?YT?JFY?UNEEF

    Which is correct for the shift but if i try to include these 2 elements the output changes and I end up with everything being displayed up to the first space, then nothing after that. So basically this is as good as I can get it at this stage.

    Any help/advice would be hugely appreciated.

    Thanks Guys
    you don't want ' ' to be shifted, isn't it?
    Then why don't you add just a

    Code:
    if (input!=' ') {do everything you want, shift etc}
    else{ printf("%c",input);}
    you could try to add also &&isalpha(input) into the if..

    what do you think?

  3. #3
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    I have tried putting in if (input != ' ') { but whenever I do It does not seem to produce the output that I desire, it will only accept the input up to to the first space then and thats it so i am left with the following:

    input: hi my name is trev
    output: hi

    or it goes into a continuous loop or it produces output completely different then what it should be. So im pretty stuck, but i know it it something simple that I am not seeing so i will keep on chipping away at it. If i figure it out ill post it

    cheers guys

  4. #4
    * noops's Avatar
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    Don't use scanf, use fgets.

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    Yeh I have heard that scanf() can be a bit of a dog. We have not been introduced to fgets yet but i will look into it.

    cheers

  6. #6
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    You should use "islower()". Remember, these charactor type functions return NON-ZERO for true. So you could do:

    if(islower(c) != 0)
    x = toupper(c);

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by rmetcalf View Post
    You should use "islower()". Remember, these charactor type functions return NON-ZERO for true. So you could do:

    if(islower(c) != 0)
    x = toupper(c);
    How can that help? If islower(c) is false, toupper(c) == c by definition.

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    It only converts it if it is NOT equal to zero

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by rmetcalf View Post
    It only converts it if it is NOT equal to zero
    I didn't make myself clear. This:
    Code:
    x = toupper(c);
    and this:
    Code:
    if (islower(c) != 0)
        x = toupper(c);
    are completely and totally exactly the same, except that in the first case x will be defined no matter what, and in the second x will be random garbage if c is not a lower-case letter. If you want ' ' to stay ' ', you'll probably want to do the first, since x will be ' ' afterwards, and not the second, where x will be the same letter as before the space (and hence it will appear twice in the output).

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    Let's start from the beginning. The issue is that when presented with a string we want to convert lower case letters to uppercase letters without effecting any other charactor types.

    This means:

    islower('c') returns non-zero - convert it to upper case.
    islower('F') returns zero - leave it alone.
    islower('#') returns zero - leave it alone.

    So, since the function islower() returns non-zero when the argument is a lower case letter the following loop will correctly process the string:

    for(ct = 0; ct < strlen(str); ++ ct)
    if(islower(str[ct]) != 0)
    str[ct] = toupper(str[ct]);

    The result will not contain any lower case letters yet any other type of character will remain as it was.

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by rmetcalf View Post
    Let's start from the beginning. The issue is that when presented with a string we want to convert lower case letters to uppercase letters without effecting any other charactor types.

    This means:

    islower('c') returns non-zero - convert it to upper case.
    islower('F') returns zero - leave it alone.
    islower('#') returns zero - leave it alone.

    So, since the function islower() returns non-zero when the argument is a lower case letter the following loop will correctly process the string:

    for(ct = 0; ct < strlen(str); ++ ct)
    if(islower(str[ct]) != 0)
    str[ct] = toupper(str[ct]);

    The result will not contain any lower case letters yet any other type of character will remain as it was.
    Just for fun, run the loop
    Code:
    for(ct = 0; ct < strlen(str); ++ct)
        str[ct] = toupper(str[ct]);
    and compare with your version. One of us will be surprised.

  12. #12
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    Your loop will work as well, and actually is more elegant.

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