Harvard CS50 学习笔记（二）

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for (i = 0, n = strlen(str); i < n; i++) {
  ......
}

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#include <stdio.h>

int main(int argc, string argv[])
{
    ...
}

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#include <stdio.h>

int main(int argc, string argv[])
{
   if (argc == 2) {
     printf("hello, %s\n", argv[1]);
   } else {
     printf("hello. world\n");
   }
}

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#include <stdio.h>

int main(int argc, string argv[])
{
   if (argc != 2) {
     printf("Missing command-line argument!\n");
     return 1;
   printf("hello, %s\n", argv[1]);
     return 0;
}

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

// declare functions
string getInput(int player);
int calculateScores(string input);
void compareAndOutput(int score1, int score2);

char letterArr[26] = {'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  numArr[26] = {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};

int main(void) {
    // get user input
    string player1 = getInput(1);
    string player2 = getInput(2);

    // calculate scores
    int player1Score = calculateScores(player1);
    int player2Score = calculateScores(player2);

    // compare and output
    compareAndOutput(player1Score, player2Score);
}

string getInput(int player) {
    return get_string("Player %i: ", player);
}

int calculateScores(string input) {
    int sum = 0;
    for (int i = 0, length = strlen(input); i < length; i++) {
        for (int j = 0; j < 26; j++) {
            char letter = toupper(input[i]);
            if (letter == letterArr[j]) {
                sum += numArr[j];
        }
    }
    }
    return sum;
}

void compareAndOutput(int score1, int score2) {
    if (score1 > score2) {
        printf("Player 1 wins!\n");
    } else if (score1 < score2) {
        printf("Player 2 wins!\n");
    } else {
        printf("Tie!\n");
    }
}

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

// declare finctions
string getInput();
int countLetters(string text);
int countSentences(string text);
int countWords(string text);
void calculatteGrade(int letterCount, int sentenceCount, int wordCount);

int main(void) {
    // getInput
    string text = getInput();

    // count letters
    int letterCount = countLetters(text);

    // count sentences
    int sentenceCount = countSentences(text);

    // count words
    int wordCount = countWords(text);

    // calculate grade
    calculatteGrade(letterCount, sentenceCount, wordCount);

}

string getInput() {
    return get_string("Text: ");
}

int countLetters(string text) {
    int letterCount = 0;
    for (int i = 0, n = strlen(text); i < n; i++) {
        if (text[i] >= 'A' && text[i] <= 'z') {
            letterCount++;
        }
    }
    return letterCount;
}

int countSentences(string text) {
    int sentenceCount = 0;
    for (int i = 0, n = strlen(text); i < n; i++) {
        if (text[i] == '!' || text[i] == '.' || text[i] == '?') {
            sentenceCount++;
        }
    }
    return sentenceCount;
}

int countWords(string text) {
    int wordCount = 0;
    for (int i = 0, n = strlen(text); i < n; i++) {
        if (text[i] == ' ') {
            wordCount++;
        }
    }
    return ++wordCount;
}

void calculatteGrade(int letterCount, int sentenceCount, int wordCount) {
    // 这里有个坑，C 不会自动转换类型，int 运算后结果还是 int，即便结果我用double 类型接收，需要手动转换，或者在运算中加入浮点型
    double averageLetterCount = letterCount * 100.0 / wordCount;
    double averageSentenceCount = sentenceCount * 100.0 / wordCount;
    int grade = round(0.0588 * averageLetterCount - 0.296 * averageSentenceCount - 15.8);
    if (grade < 1) {
        printf("Before Grade 1\n");
    } else if (grade >=16) {
        printf("Grade 16+\n");
    } else {
        printf("Grade %i\n", grade);
    }
}

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

// delcare functions
int judgeArgument(int argc, string argv[]);
void encryptTheInput();
int checkLength(int argc, string argv[]);
int checkLetter(string str);
int checkDuplicate(string str);


string key = "";

int main(int argc, string argv[]) {
    // judge argument
    if (judgeArgument(argc, argv) != 0) {
        return 1;
    } else {
        // crypt the input
        encryptTheInput();
        return 0;
    }
}

int judgeArgument(int argc, string argv[]) {
    if (checkLength(argc, argv) != 0) {
        return 1;
    } else {
        string str = argv[1];
        if (checkLetter(str) != 0) {
            return 1;
        } else {
            if (checkDuplicate(str) != 0) {
                return 1;
            }
        }
    }
    key = argv[1];
    return 0;
}

int checkLength(int argc, string argv[]) {
    if (argc != 2) {
        printf("Usage: ./substitution key\n");
        return 1;
    } else {
        string str = argv[1];
        int length = strlen(str);
        if (length != 26) {
            printf("Key must contain 26 characters.\n");
            return 1;
        }
    return 0;
}
}

int checkLetter(string str) {
    int length = strlen(str);
    for (int i = 0; i < length; i++) {
        if (str[i] < 'A' || str[i] > 'z') {
            return 1;
        } else if (str[i] > 'Z' && str[i] < 'a') {
            return 1;
        }
    }
    return 0;
}

int checkDuplicate(string str) {
    int length = strlen(str);
    for (int i = 0; i < length; i++) {
        for (int j = 0; j < length; j++) {
            if (i != j) {
                if (str[i] == str[j]) {
                return 1;
            }
            }
        }
    }
    return 0;
}

void encryptTheInput() {
    string input = get_string("plaintext:  ");
    int length = strlen(input);
  	// 这里有个大坑，就是如果输出的加密信息，不是字符串类型，而直接使用数组，那么会出现分割问题，部分结果最后可能会多 ‘\n’，无法通过检测
    string output = input;
    for (int i = 0; i < length; i++) {
        if (input[i] >= 'A' && input[i] <= 'Z') {
            int index = input[i] - 'A';
            output[i] = toupper(key[index]);
        } else if (input[i] >= 'a' && input[i] <= 'z') {
            int index = input[i] - 'a';
            output[i] = tolower(key[index]);
        }
    }
    printf("ciphertext: %s", output);
    printf("\n");
}