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

Quote:

---

Originally Posted by trevordunstan

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?

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

Don't use scanf, use fgets.

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

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);

Quote:

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Originally Posted by rmetcalf

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.

It only converts it if it is NOT equal to zero

Quote:

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Originally Posted by rmetcalf

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).

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.

Quote:

---

Originally Posted by rmetcalf

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.

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