Rotating alphabetical characters by 26

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[dm_code_snippet background=”no” background-mobile=”yes” slim=”yes” line-numbers=”yes” bg-color=”#abb8c3″ theme=”dark” language=”clike” wrapped=”yes” height=”” copy-text=”Copy Code” copy-confirmed=”Copied”]

#include<stdio.h>
#include<cs50.h>
#include<string.h>
#include<ctype.h>
int main(void) 
{
  string name = get_string("Enter: ");
  printf("Entered text by user: %s\n", name);
  int n = strlen(name);
  printf("lenght of entered text: %i\n", n);
  int key = get_int("enter key: ");
  for (int i = 0; i < n; i++) 
  {
    if (isalpha(name[i])) 
    {
      if (name[i] + key >= 91) 
      {
        name[i] = (name[i] + key - 26);
      } 
      else 
      {
        name[i] = (name[i] + key);
      }
    } 
    else 
    {
      name[i] = name[i];
    }
  }
  printf("cipher text: %s\n", name);
}

[/dm_code_snippet]

Above is my code for uppercase characters (I am assuming for the time being the user enters only uppercase characters and not lowercase) only which is still faulty (https://www.canva.com/design/DAE1xXhyoXk/ba5X0Pf7gSAkmh9LdkbuOQ/view?utm_content=DAE1xXhyoXk&utm_campaign=designshare&utm_medium=link&utm_source=sharebutton).

Up to key 44 or {72 which is ASCII of H + 44) = 116, the code working. So now perhaps need to introduce % operator correctly for rotation between 65 to 90.

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Reply

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1 % 26 = 1 , essentially if k is < n:

k % n = k

But

How about n % n = ?

Or: n + 1 % n = ? n + 2 % n = ? n + 3 % n = ? …

You should even try out: 2n % n 2n + 1 % n …

Try it out! See the pattern? Good luck!

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Thanks.

Though still far from coming out with the pattern, here is my intermittent code:

[dm_code_snippet background=”yes” background-mobile=”no” slim=”yes” line-numbers=”yes” bg-color=”#abb8c3″ theme=”dark” language=”clike” wrapped=”yes” height=”” copy-text=”Copy Code” copy-confirmed=”Copied”]

#include<stdio.h>
#include<cs50.h>
#include<string.h>
#include<ctype.h>

int main(void)

{
  string name = get_string("Enter: ");
  printf("Entered text by user: %s\n", name);
  int n = strlen(name);
  printf("lenght of entered text: %i\n", n);
  int key = get_int("enter key: ");
  for (int i = 0; i < n; i++)
  {
    if (isalpha(name[i]))
    {
      if (name[i] + key > 90 && name[i] + key < 143)
      {
        name[i] = (name[i] + key - 26);
      }
      if (name[i] + key > 142 && name[i) + key < 195)
      {
        name[i] = (name[i] + key - 52);
      } 
      else
      {
        name[i] = (name[i] + key);
      }
    } 
    else
    {
      name[i] = name[i];
    }
  }
  printf("cipher text: %s\n", name);
}

[/dm_code_snippet]

My intention was to make the code work up to cycle that begins with 143 up to 194. I am surprised to see that up to key 18, the code works (z cipher text). But as I enter key 19, I get T as cipher text:

Instead of if (isalpha(name[i])), can isalpha be replaced by a CS50 function that will spot instead of letters, uppercase letters/lowercase letters. I tried with if (uppercase(name[i])), but did not work.

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Reply

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Yes isupper, and islower under I believe the ctype library

Use this next time, and remember, they give you clues on the pset itself.

https://manual.cs50.io/

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Reply

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https://edstem.org/us/courses/176/discussion/1004831?comment=2311979

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