---
tags: CS50
---
# (2022年) CS50 week2
其實之前就已經修完 CS50 了，不過因應 2022 年將課堂作業的系統
從 c9.io 換到 github codespace + vscode 整合
打算來重溫一下裡面的作業，並暖身一下 C 語言的手感
由於已經有許多前輩分享課程與作業的心得
加上官網教材的投影片、重點筆記、教學影片都非常完整
故不再做詳細的紀錄，專注在作業 (Lab, Problem sets) 上面
https://cs50.harvard.edu/x/2022/weeks/2/
---
### Lab2: [Scrabble](https://cs50.harvard.edu/x/2022/labs/2/)
:::spoiler (點擊展開) 符合 `style50` 風格的程式碼
```c
#include <ctype.h>
#include <cs50.h>
#include <stdio.h>
#include <string.h>
// Points assigned to each letter of the alphabet
int POINTS[] = {1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3, 1, 1, 3, 10, 1, 1, 1, 1, 4, 4, 8, 4, 10};
/* A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z */
int compute_score(string word);
int main(void)
{
// Get input words from both players
string word1 = get_string("Player 1: ");
string word2 = get_string("Player 2: ");
// Score both words
int score1 = compute_score(word1);
int score2 = compute_score(word2);
if (score1 > score2)
{
printf("Player 1 wins!\n");
}
else if (score1 < score2)
{
printf("Player 2 wins!\n");
}
else
{
printf("Tie!\n");
}
}
int compute_score(string word)
{
int sum = 0;
for (int i = 0, n = strlen(word); i < n; i++)
{
// in ASCII, A ~ Z is 65 ~ 90, so only collect char code 65 ~ 90
char c = toupper(word[i]);
// -65 for get index (condition is 0 ~ 25)
int c_index = (int) c - 65;
// accumulate score in valid char
if (c_index >= 0 && c_index < 26)
{
sum += POINTS[c_index];
}
}
return sum;
}
```
:::
--
:::spoiler (點擊展開) 個人覺得比較好讀的程式碼風格
```c
#include <ctype.h>
#include <cs50.h>
#include <stdio.h>
#include <string.h>
// Points assigned to each letter of the alphabet
int POINTS[] = {1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3, 1, 1, 3, 10, 1, 1, 1, 1, 4, 4, 8, 4, 10};
/* A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z */
int compute_score(string word);
int main(void)
{
// Get input words from both players
string word1 = get_string("Player 1: ");
string word2 = get_string("Player 2: ");
// Score both words
int score1 = compute_score(word1);
int score2 = compute_score(word2);
if (score1 > score2)
printf("Player 1 wins!\n");
if (score1 < score2)
printf("Player 2 wins!\n");
if (score1 == score2)
printf("Tie!\n");
}
int compute_score(string word)
{
int sum = 0;
for (int i = 0, n = strlen(word); i < n; i++) {
// in ASCII, A ~ Z is 65 ~ 90, so only collect char code 65 ~ 90
char c = toupper(word[i]);
// -65 for get index (condition is 0 ~ 25)
int c_index = (int) c - 65;
// accumulate score in valid char
if (c_index >= 0 && c_index < 26)
sum += POINTS[c_index];
}
return sum;
}
```
:::
--
執行
驗證
---
### 作業： [Readability](https://cs50.harvard.edu/x/2022/psets/2/readability/)
:::spoiler (點擊展開) 符合 `style50` 風格的程式碼
```c
#include <ctype.h>
#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
int main(void)
{
string text = get_string("Text: ");
int letter_count = 0;
int word_count = strlen(text) > 0 ? 1 : 0;
int sentence_count = 0;
for (int i = 0, n = strlen(text); i < n; i++)
{
char c = toupper(text[i]);
// count letters (in ASCII, A ~ Z is 65 ~ 90)
if (c >= 65 && c <= 90)
{
letter_count += 1;
}
// count sentences (in '!', '.', '?)
if (c == '!' || c == '.' || c == '?')
{
sentence_count += 1;
}
// count words (in ' ')
if (c == ' ')
{
word_count += 1;
}
}
// formula: Coleman-Liau index
// index = 0.0588 * L - 0.296 * S - 15.8
// L is the average number of letters per 100 words in the text
// S is the average number of sentences per 100 words in the text
float L = letter_count / (float) word_count * 100;
float S = sentence_count / (float) word_count * 100 ;
float CL_index = 0.0588 * L - 0.296 * S - 15.8;
if (CL_index < 1)
{
printf("Before Grade 1\n");
}
else if (CL_index >= 16)
{
printf("Grade 16+\n");
}
else
{
printf("Grade %i\n", (int) round(CL_index));
}
}
```
:::
--
:::spoiler (點擊展開) 個人覺得比較好讀的程式碼風格
```c
#include <ctype.h>
#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
int main(void)
{
string text = get_string("Text: ");
int letter_count = 0;
int word_count = strlen(text) > 0 ? 1 : 0;
int sentence_count = 0;
for (int i = 0, n = strlen(text); i < n; i++) {
char c = toupper(text[i]);
// count letters (in ASCII, A ~ Z is 65 ~ 90)
if (c >= 65 && c <= 90)
letter_count += 1;
// count sentences (in '!', '.', '?)
if (c == '!' || c == '.' || c == '?')
sentence_count += 1;
// count words (in ' ')
if (c == ' ')
word_count += 1;
}
// formula: Coleman-Liau index
// index = 0.0588 * L - 0.296 * S - 15.8
// L is the average number of letters per 100 words in the text
// S is the average number of sentences per 100 words in the text
float L = letter_count / (float) word_count * 100;
float S = sentence_count / (float) word_count * 100 ;
float CL_index = 0.0588 * L - 0.296 * S - 15.8;
if (CL_index < 1)
printf("Before Grade 1\n");
else if (CL_index >= 16)
printf("Grade 16+\n");
else
printf("Grade %i\n", (int) round(CL_index));
}
```
:::
--
執行
驗證
---
### 作業： [Caesar](https://cs50.harvard.edu/x/2022/psets/2/caesar/)
:::spoiler (點擊展開) 符合 `style50` 風格的程式碼
```c
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, string argv[])
{
// argc[1] must be present
if (argc != 2)
{
printf("Usage: ./caesar key\n");
return 1;
}
// argc[1] all value must be digit (decimal number)
string input_key = argv[1];
for (int i = 0, n = strlen(input_key); i < n; i++)
{
if (isdigit(input_key[i]) == 0)
{
printf("Usage: ./caesar key\n");
return 1;
}
}
// just need get alphabet number (0 ~ 25)
int key = atoi(argv[1]) % 26;
string plaintext = get_string("plaintext: ");
string ciphertext = plaintext;
// for lopp to convert char
for (int i = 0, n = strlen(ciphertext); i < n; i++)
{
// covert alphabet only
char c = ciphertext[i];
if (isalpha(c))
{
// if isupper = 65, islower = 97
int alpha_params = isupper(c) ? 65 : 97;
c = (c + key - alpha_params) % 26 + alpha_params;
// do convert alphabet
ciphertext[i] = c;
}
}
printf("Ciphertext: %s\n", ciphertext);
}
```
:::
--
:::spoiler (點擊展開) 個人覺得比較好讀的程式碼風格
```c
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, string argv[])
{
// argc[1] must be present
if (argc != 2) {
printf("Usage: ./caesar key\n");
return 1;
}
// argc[1] all value must be digit (decimal number)
string input_key = argv[1];
for (int i = 0, n = strlen(input_key); i < n; i++) {
if (isdigit(input_key[i]) == 0) {
printf("Usage: ./caesar key\n");
return 1;
}
}
// just need get alphabet number (0 ~ 25)
int key = atoi(argv[1]) % 26;
string plaintext = get_string("plaintext: ");
string ciphertext = plaintext;
// for lopp to convert char
for (int i = 0, n = strlen(ciphertext); i < n; i++) {
// covert alphabet only
char c = ciphertext[i];
if (isalpha(c)) {
// if isupper = 65, islower = 97
int alpha_params = isupper(c) ? 65 : 97;
c = (c + key - alpha_params) % 26 + alpha_params;
// do convert alphabet
ciphertext[i] = c;
}
}
printf("Ciphertext: %s\n", ciphertext);
}
```
:::
--
執行
驗證
---
### 作業： [Substitution](https://cs50.harvard.edu/x/2022/psets/2/substitution/)
:::spoiler (點擊展開) 符合 `style50` 風格的程式碼
```c
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
char indexOfalphabets(char c, string alphabets_string)
{
int index = -1;
for (int i = 0, n = strlen(alphabets_string); i < n; i++)
{
if (toupper(alphabets_string[i]) == toupper(c))
{
index = i;
}
}
return index;
}
int main(int argc, string argv[])
{
// argc[1] must be present
if (argc != 2)
{
printf("Usage: ./substitution key\n");
return 1;
}
// count length of chars
string input_string = argv[1];
int input_char_count = 0;
for (int i = 0, n = strlen(input_string); i < n; i ++)
{
char c = input_string[i];
int index = indexOfalphabets(c, input_string);
if (isalpha(c) && index == i)
{
input_char_count += 1;
}
}
// argc[1] must be 26 length of chars
if (input_char_count != 26)
{
printf("Key must contain 26 characters.");
return 1;
}
// conver input params to array
string alphabets_string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int input_char_arr[26];
for (int i = 0; i < 26; i++)
{
char c = toupper(input_string[i]);
int diff = c - alphabets_string[i];
input_char_arr[i] = diff;
}
string plaintext = get_string("plaintext: ");
string ciphertext = plaintext;
// for lopp to convert char
for (int i = 0, n = strlen(ciphertext); i < n; i++)
{
char c = ciphertext[i];
int index_of_alphabets = indexOfalphabets(c, alphabets_string);
int chiper_params = input_char_arr[index_of_alphabets];
// covert alphabet only
if (isalpha(c))
{
char cipher_char = c + chiper_params;
// do convert alphabet
ciphertext[i] = cipher_char;
}
}
printf("ciphertext: %s\n", ciphertext);
}
```
:::
--
:::spoiler (點擊展開) 個人覺得比較好讀的程式碼風格
```c
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
char indexOfalphabets(char c, string alphabets_string)
{
int index = -1;
for (int i = 0, n = strlen(alphabets_string); i < n; i++) {
if (toupper(alphabets_string[i]) == toupper(c))
index = i;
}
return index;
}
int main(int argc, string argv[])
{
// argc[1] must be present
if (argc != 2) {
printf("Usage: ./substitution key\n");
return 1;
}
// count length of chars
string input_string = argv[1];
int input_char_count = 0;
for (int i = 0, n = strlen(input_string); i < n; i ++) {
char c = input_string[i];
int index = indexOfalphabets(c, input_string);
if (isalpha(c) && index == i)
input_char_count += 1;
}
// argc[1] must be 26 length of chars
if (input_char_count != 26) {
printf("Key must contain 26 characters.");
return 1;
}
// conver input params to array
string alphabets_string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int input_char_arr[26];
for (int i = 0; i < 26; i++) {
char c = toupper(input_string[i]);
int diff = c - alphabets_string[i];
input_char_arr[i] = diff;
}
string plaintext = get_string("plaintext: ");
string ciphertext = plaintext;
// for lopp to convert char
for (int i = 0, n = strlen(ciphertext); i < n; i++)
{
char c = ciphertext[i];
int index_of_alphabets = indexOfalphabets(c, alphabets_string);
int chiper_params = input_char_arr[index_of_alphabets];
// covert alphabet only
if (isalpha(c)) {
char cipher_char = c + chiper_params;
// do convert alphabet
ciphertext[i] = cipher_char;
}
}
printf("ciphertext: %s\n", ciphertext);
}
```
:::
--
執行
驗證
Sign in with Wallet
Connect another wallet