initial commit

pset1/cash/cash.c

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+// Pset1 - cash
+// A program that prompts users for a value in dollars
+// and returns a value that represents the minimal amount of coins this dollar value can be reached
+
+#include <math.h> // round()
+#include <cs50.h> // get_float
+#include <stdio.h>
+
+int main(void)
+{
+    // 1 - prompt user for value in dollars (d)
+    float d;
+    do
+    {
+        d = get_float("Change owed: ");
+    }
+    while (d < 0); // reprompt if value is negative
+
+    // 2 - convert dollars to cents (c)
+    int c = round(d * 100);
+
+    // 3 - algorithm to determine least amount of coins
+
+    // 3 - 1 25c quarter (q)
+    int q = c / 25;
+    int x = c - q * 25;
+
+    // 3 - 2 10c dime (m)
+    int m = (x / 10);
+    x = x - m * 10;
+
+    // 3 - 3 5c nickel (n)
+    int n = (x / 5);
+    x = x - n * 5;
+
+    // 3 - 4 1c penny (p)
+    int p = (x / 1);
+    x = x - p;
+
+    // 4 total (t) the number of each coin and print this value as minimal number of coins
+    int t = q + m + n + p;
+    printf("%i\n", t);
+}

pset1/credit/credit.c

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+// Pset1 - credit
+// design a program to prompt user for a credit card number then report whether it is American Express, Visa, Mastercard, or invalid.
+
+// 1 - prompt user
+// 2 - checksum
+// 3 - count number of digits
+// 4 - if and else conditions to filter for VISA, AMEX, or MASTERCARD
+
+#include <cs50.h> // get_long_long
+#include <stdio.h>
+
+int main(void)
+{
+    // 1.0 Prompt user for a credit card number (cc)
+    long long cc = get_long_long("Number: ");
+
+    // 2.0 Checksum
+    // 2.1 Define new variables
+    long long cc1 = cc;                      // copy cc so it remains unchanged as cc1 will be updated
+    int checksum = 0;                        // starting value of checksum
+
+    // 2.2 while() loop to perform checksum arithmetic
+    while (cc1 > 0)
+    {
+        int a = cc1 % 10;                    // get first digit (to be added to checksum, +checksum)
+        cc1 = cc1 / 10;
+
+        int b = cc1 % 10 * 2;                // get second-to-last digit and mulitply by 2 (may result in 2 digits)
+        int c = b % 10;                      // get last digit of a (+checksum)
+        int d = b / 10 % 10;                 // get first digit of a (+checksum)
+
+        checksum = checksum + a + c + d;
+        cc1 = cc1 / 10;
+
+    }
+
+    // 3.0 Count number of digits using while loop
+    long long cc2 = cc;                      // same principle as cc1
+    int digit = 0;                           // digit counter
+
+    while (cc2 > 0)
+    {
+        cc2 = cc2 / 10;
+        digit++;
+    }
+
+    // 4.0 VISA, AMEX, or MASTERCARD?
+    if (checksum % 10 == 0)                  // Select for numbers that pass checksum
+    {
+        // Select for numbers with digits 13, 15, OR 16 then sort further
+        if (digit == 13)                     // Select for 13-digit number
+        {
+            if (cc / 1000000000000 == 4)
+            {
+                printf("VISA\n");
+            }
+            else
+            {
+                printf("INVALID\n");
+            }
+        }
+        else if (digit == 15)               // Select for 15-digit number
+        {
+            if (cc / 10000000000000 == 34 || cc / 10000000000000 == 37)
+            {
+                printf("AMEX\n");
+            }
+            else
+            {
+                printf("INVALID\n");
+            }
+        }
+        else if (digit == 16)              // Select for 16-digit number
+        {
+            int mc = cc / 100000000000000;
+            if (mc == 51 || mc == 52 || mc == 53 || mc == 54 || mc == 55)
+            {
+                printf("MASTERCARD\n");
+            }
+            else if (cc / 1000000000000000 == 4)
+            {
+                printf("VISA\n");
+            }
+            else
+            {
+                printf("INVALID\n");
+            }
+        }
+        else
+        {
+            printf("INVALID\n");          // If number is not 13, 15, or 16 digits-long, INVALID
+        }
+    }
+    else
+    {
+        printf("INVALID\n");             // If it doesn't pass checksum, INVALID
+    }
+
+}

pset1/mario/less/mario.c

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+// pset1: Mario (less)
+// create a program, utilising printf(), that prints out a half-pyramid of a user-defined height, displayed as #
+// e.g.
+//     #
+//    ##
+//   ###
+//  ####
+// #####
+
+// Specifications: integer between 1 and 8
+
+#include <cs50.h> // for get_int()
+#include <stdio.h>
+
+int main(void)
+{
+    // do-while loop
+    int h;
+    do
+    {
+        // prompt once for integer h
+        h = get_int("Height: ");
+    }
+    // reprompt if h is not between 1 and 8
+    while (h < 1 || h > 8);
+
+    // define y, which will be used, as a separate decreasing counter with an initial value h, to determine number of spaces
+    int y = h;
+
+    // print pyramid using for loop
+    // define number of lines (pyramid height) based on h
+    for (int i = 0; i < h; i++)
+    {
+        // print spaces
+        for (int a = 1; a < y; a++)
+        {
+            printf(" ");
+        }
+        //after exiting loop (or effectively, one pyramid row), decrease value of y by 1
+        y--;
+
+        // print hashtags
+        for (int b = 0; b < i + 1; b++)
+        {
+            printf("#");
+        }
+
+        // next line
+        printf("\n");
+    }
+
+}

pset1/mario/more/mario.c

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+// pset1: Mario
+// create a program, utilising printf(), that prints out a pyramid of a user-defined height, displayed as #
+// e.g.
+//     #  #
+//    ##  ##
+//   ###  ###
+//  ####  ####
+// #####  #####
+
+// Specifications: accepts integer between 0 and 8
+
+#include <cs50.h> // for get_int()
+#include <stdio.h>
+
+int main(void)
+{
+    // do-while loop
+    int h;
+    do
+    {
+        // prompt once for integer h
+        h = get_int("Height: ");
+    }
+    // reprompt if h is not between 0 and 8
+    while (h < 1 || h > 8);
+
+    // define y, which will be used, as a separate decreasing counter with an initial value h, to determine number of spaces
+    int y = h;
+
+    // print pyramid using for loop
+    // define number of lines (pyramid height) based on h
+    for (int i = 0; i < h; i++)
+    {
+        // this block of code codes for one row of the pyramid
+        // print spaces
+        for (int a = 1; a < y; a++)
+        {
+            printf(" ");
+        }
+        //after exiting loop (or almost effectively, one pyramid row), decrease value of y by 1
+        y--;
+
+        // print hashtags (left)
+        for (int b = 0; b < i + 1; b++)
+        {
+            printf("#");
+        }
+
+        // 2 space gap
+        printf("  ");
+
+        // print hashtag (right)
+        for (int c = 0; c < i + 1; c++)
+        {
+            printf("#");
+        }
+
+        // next line
+        printf("\n");
+    }
+
+}

pset2/caesar/README.md

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+https://docs.cs50.net/2018/x/psets/2/caesar/caesar.html

pset2/caesar/caesar.c

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+// Pset2: Caesar
+// Implement program that encrypts messages using Caesar's ciper
+// idea is that the ciper (k), a non-negative integer, added to a message will return the cipher text
+
+#include <cs50.h>           // get_string
+#include <stdio.h>
+#include <stdlib.h>         // atoi
+#include <string.h>         // strlen()
+#include <ctype.h>          // isalpha, islower, isupper
+
+#define index_upper 65      // + to convert ASCII to indexed alphabet, - to conver indexed alphabet to ASCII
+#define index_lower 97      // "        "
+#define alpha_n 26          // number of alphabet letters
+
+int main(int argc, string argv[])
+{
+    // if more than one command-line argument is typed, print error message and return main value of 1
+    if (argc >= 3)
+    {
+        printf("error: please input a single secret key\n");
+        return 1;
+    }
+    else if (argc < 2)
+    {
+        printf("error: please enter secret key\n");
+        return 1;
+    }
+    else
+    {
+        // store user-input plaintext as string
+        string txt = get_string("plaintext: ");
+
+        // convert k from string to int for cipher algorithm
+        int k = atoi(argv[1]);
+
+        // for loop to scan for alphabetical characters and replace with ciphered text
+        for (int i = 0; i < strlen(txt); i++)
+        {
+            char p = txt[i];
+            if (isalpha(p))
+            {
+                if (isupper(p))
+                {
+                    // cipher algorithm + replace i-th position of text
+                    txt[i] = (p + k - index_upper) % alpha_n + index_upper;
+                }
+                else if (islower(p))
+                {
+                    // cipher algorithm + replace i-th position of text
+                    txt[i] = (p + k - index_lower) % alpha_n + index_lower;
+                }
+            }
+        }
+        // print ciphertext output
+        printf("ciphertext: %s\n", txt);
+
+        return 0;
+
+    }
+}
+

pset2/crack/README.md

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+https://docs.cs50.net/2018/x/psets/2/crack/crack.html

pset2/crack/crack.c

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+// Pset 2: Crack
+// Implement a program that cracks passwords encrypted using a "one-way hash function"
+
+#define _XOPEN_SOURCE      // crypt()
+
+#include <cs50.h>          // string
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>        // crypt()
+
+int main(int argc, string argv[])
+{
+    // 1.0a Select for valid hashed password input
+    if (argc == 2)
+    {
+        // 2.0 Extract salt from hash input
+        string hash = argv[1];
+        char b[3] = {hash[0], hash[1], '\0'};  // extract first two characters from hash input and store in array
+        string salt = b;                       // combine first two characters from hash input into a string
+
+        // 3.0 generate random plaintext to feed into crypt()
+        // 3.1 declare alphabet and empty array to store random plaintext
+        char alphabet[] = {"\0ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"};
+        char p[6] = {'\0', '\0', '\0', '\0', '\0', '\0'};
+
+        // 3.2 counter for 5th letter
+        for (int letter_five = 0; letter_five < 53; letter_five++)  // 52 is the length of variable alphabet including the initial '\0'
+        {
+            // 3.3 counter for 4th letter
+            for (int letter_four = 0; letter_four < 53; letter_four++)
+            {
+                // 3.4 counter for 3rd letter
+                for (int letter_three = 0; letter_three < 53; letter_three++)
+                {
+                    // 3.5 counter for 2nd letter
+                    for (int letter_two = 0; letter_two < 53; letter_two++)
+                    {
+                        // 3.6 counter for 1st letter
+                        for (int letter_one = 1; letter_one < 53; letter_one++)
+                        {
+                            p[0] = alphabet[letter_one];
+                            p[1] = alphabet[letter_two];
+                            p[2] = alphabet[letter_three];
+                            p[3] = alphabet[letter_four];
+                            p[4] = alphabet[letter_five];
+
+                            if (strcmp(hash, crypt(p, salt)) == 0)
+                            {
+                                printf("%s\n", p);
+                                return 0;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        printf("hash: %s\n", hash);
+        return 0;
+    }
+    // 1.0b If invalid input, print error message and return 1
+    else
+    {
+        printf("error: input valid hashed password\n");
+        return 1;
+    }
+}