CS50 Vigenere

vigenere.c

/* CS50 solution. Feel free to check with any online compiler. To get credit from Harvard you may have to make a few changes.
hmu at s.velaga@uky.edu if you have any questions. Also I haven't learned about proper code style and formatting - 
if you wanna hmu to tell me this looks like shit and how to make it look better pls do */

#include <stdio.h> //includes fget and stdin // 
#include <ctype.h> // used for isupper, islower, toupper, tolower
#include <stdlib.h>
#include <string.h> //used for strlen  

int main()

{   
    // Asks the user for some plaintext to cipher //
    
    char plaintext[100];
    
    printf("\nPlease enter some text that you want encrypted. . . . ");
    fgets(plaintext,sizeof(plaintext),stdin);
    
    // Asks the user to enter in a keyword (k) that will be used as a key //
    
    char k[50];
    
    printf("\nPlease enter some keyword that will be used as your key. . . . ");
    fgets(k,sizeof(plaintext),stdin);
    
    // loops through the key and assigns each charater in the key to an integer
    // from 0 - 26 for the letters in the alphabet
    
    int knum[50];
    int klen; // is the length of the keyword
    klen = strlen(k) -1;
    
    for (int i = 0, klen = strlen(k); i < klen; i++)
        {
            if (k[i]>= 'A' && k[i] <= 'Z')
                {
                    knum[i] = k[i] - 65;
                }
            else if (k[i] >= 'a' && k[i] <= 'z')
                {
                    knum[i] = k[i] - 97;
                }
        }
    
    printf("\n\n");
    
    // get the ciphertext by adding the plain text values to the keyword values //
    
    int m;
    int j;
    int plaintextnum[100];
    
    for (j = 0, m = strlen(plaintext); j < m; j++)
        {
            if (plaintext[j] >= 'A' && plaintext[j] <= 'Z')
                {
                 plaintextnum[j] = (plaintext[j] + knum[j % klen]);
                 
                if (plaintextnum[j] > 90)
                    {
                        plaintextnum[j] = plaintextnum[j] - 26;
                    }
                else 
                    { 
                        plaintextnum[j] = plaintextnum[j];
                    }
                        
                printf("%c", plaintextnum[j]);
                }
            else if (plaintext[j] >= 'a' && plaintext[j] <= 'z')
                {
                    plaintextnum[j] = (plaintext[j] + knum[j % klen]);
                    
                    if (plaintextnum[j] > 96 && plaintextnum[j] < 123)
                        {
                            plaintextnum[j] = plaintextnum[j];
                        }
                    else 
                        { 
                            plaintextnum[j] = plaintextnum[j] - 26;
                        }
                    printf("%c", plaintextnum[j]);
                }

        }
    return 0;