pset 2

readability

Implement a program using the Coleman-Liau index to compute the approximate grade level needed to comprehend some text, per the below.

$ ./readability
Text: Congratulations! Today is your day. You're off to Great Places! You're off and away!
Grade 3

readability.c

#include <stdio.h>
#include <cs50.h>
#include <math.h>

int count_letters(string s);
int count_words(string s);
int count_sentences(string s);

int main(void)
{
    string text = get_string("Text: ");
    int letters = count_letters(text);
    int words = count_words(text);
    int sentences = count_sentences(text);
    double L = ((double) letters / words) * 100;
    double S = ((double) sentences / words) * 100;
    double i = 0.0588 * L - 0.296 * S - 15.8;
    int index = round(i);

    if (index < 1)
    {
        printf("Before Grade 1\n");
    }
    else if (index >= 16)
    {
        printf("Grade 16+\n");
    }
    else
    {
        printf("Grade %i\n", index);
    }
}

int count_letters(string s)
{
    int count = 0;
    for (int i = 0; s[i] != '\0'; i++)
    {
        if ((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z'))
        {
            count++;
        }
    }

    return count;
}

int count_words(string s)
{
    int count = 0;
    for (int i = 0; s[i] != '\0'; i++)
    {
        if (s[i] == ' ')
        {
            count++;
        }
    }

    return count + 1;
}

int count_sentences(string s)
{
    int count = 0;
    for (int i = 0; s[i] != '\0'; i++)
    {
        if (s[i] == '.' || s[i] == '!' || s[i] == '?')
        {
            count++;
        }
    }

    return count;
}

substitution

Implement a program that implements a substitution cipher, per the below.

$ ./substitution JTREKYAVOGDXPSNCUIZLFBMWHQ
plaintext:  HELLO
ciphertext: VKXXN

substitution.c

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

int main(int argc, string argv[])
{
    if (argc == 2)
    {
        int slen = strlen(argv[1]);
        if (slen != 26)
        {
            printf("Key must contain 26 characters\n");
            return 1;
        }
        else
        {
            for (int i = 0; i < slen; i++)
            {
                if ((argv[1][i] > 0 && argv[1][i] < 'A') || (argv[1][i] > 'Z' && argv[1][i] < 'a') || (argv[1][i] > 'z'))
                {
                    printf("Key must contain alphabets only\n");
                    return 1;
                }
            }

            for (int i = 0; i < slen; i++)
            {
                for (int j = 0; j < slen; j++)
                {
                    if (i == j)
                    {
                        continue;
                    }
                    else if (toupper(argv[1][i]) == toupper(argv[1][j]))
                    {
                        printf("Key must contain 26 unique letters\n");
                        return 1;
                    }
                }
            }
        }

        string plaintext = get_string("plaintext: ");
        printf("ciphertext: ");
        for (int i = 0; plaintext[i] != '\0'; i++)
        {
            if (isupper(plaintext[i]))
            {
                if (isupper(argv[1][plaintext[i] - 'A']))
                {
                    printf("%c", argv[1][plaintext[i] - 'A']);
                }
                else
                {
                    printf("%c", toupper(argv[1][plaintext[i] - 'A']));
                }
            }
            else if (islower(plaintext[i]))
            {
                if (islower(argv[1][plaintext[i] - 'a']))
                {
                    printf("%c", argv[1][plaintext[i] - 'a']);
                }
                else
                {
                    printf("%c", tolower(argv[1][plaintext[i] - 'a']));
                }
            }
            else
            {
                printf("%c", plaintext[i]);
            }
        }
        printf("\n");

        return 0;
    }
    else
    {
        printf("Usage: ./substitution key\n");
        return 1;
    }
}