CS50实验2代码问题求助：无论输入何种内容均显示平局

问题现象 #

完成CS50实验2时，代码可运行但存在异常：输入提示正常显示，但无论输入什么内容，结果始终为平局。

原代码 #

#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};

int compute_score(string word1, string word2);

int main(void)
{
    int i=0, j=0;
    // Get input words from both players
    string word1 = get_string("Player 1: ");
    string word2 = get_string("Player 2: ");

    // Convert to uppercase
    int toupper(int word1);
    int toupper(int word2);

    // Score both words
    int score = compute_score(word1, word2);
    // TODO: Print the winner
    if (score == 1) {
        printf("Player 1 Wins!");
    }
    else if (score == 2) {
        printf("Player 2 Wins!");
    }
    else {
        printf("Tie!");
    }
    printf("\n");
}

int compute_score(string word1, string word2)
{
    int i, j, k, n1=strlen(word1), n2=strlen(word2), p1=0, p2=0;
    const int alphabetSize = 26;
    char letters[] = {'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'};
    for (i=0; i<n1 + n2; i++) {
        for (j=0; j<alphabetSize; j++) {
            if (letters[j] == word1[i]) {
                p1 += POINTS[j];
            }
        }
        for (k=0; k<alphabetSize; k++) {
            if (letters[k] == word2[i]) {
                p2 += POINTS[k];
            }
        }

    }
    if (p1 > p2) {
        return 1;
    }
    else if (p1 < p2) {
        return 2;
    }
    else {
        return 3;
    }
}

错误分析 #

1. 大小写转换无效：int toupper(int word1);是函数声明而非调用，toupper仅处理单个字符，需遍历每个字符完成转换，否则输入小写字母时无法与letters数组中的大写字母匹配，得分始终为0。
2. 循环逻辑错误：for(i=0; i<n1 + n2; i++)会导致索引超出单词长度，访问内存垃圾值，且无法正确遍历两个单词的所有字符，最终得分计算错误。
3. 字符匹配冗余且易出错：手动定义letters数组进行匹配效率低，且未处理非字母字符的情况。

修复后的代码 #

#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};

int compute_score(string word1, string word2);

int main(void)
{
    // Get input words from both players
    string word1 = get_string("Player 1: ");
    string word2 = get_string("Player 2: ");

    // Convert to uppercase
    for (int i = 0; word1[i] != '\0'; i++) {
        word1[i] = toupper(word1[i]);
    }
    for (int i = 0; word2[i] != '\0'; i++) {
        word2[i] = toupper(word2[i]);
    }

    // Score both words
    int score = compute_score(word1, word2);
    
    // Print the winner
    if (score == 1) {
        printf("Player 1 Wins!");
    }
    else if (score == 2) {
        printf("Player 2 Wins!");
    }
    else {
        printf("Tie!");
    }
    printf("\n");
}

int compute_score(string word1, string word2)
{
    int p1 = 0, p2 = 0;

    // Calculate score for Player 1
    for (int i = 0; word1[i] != '\0'; i++) {
        if (isalpha(word1[i])) {
            int index = word1[i] - 'A';
            p1 += POINTS[index];
        }
    }

    // Calculate score for Player 2
    for (int i = 0; word2[i] != '\0'; i++) {
        if (isalpha(word2[i])) {
            int index = word2[i] - 'A';
            p2 += POINTS[index];
        }
    }

    if (p1 > p2) {
        return 1;
    }
    else if (p1 < p2) {
        return 2;
    }
    else {
        return 3;
    }
}

修复说明 #

• 替换无效的大小写转换代码，通过循环遍历每个字符完成大写转换；
• 拆分循环，分别遍历两个单词计算得分，避免索引越界；
• 利用ASCII码直接计算字母在POINTS数组中的索引，简化匹配逻辑，同时通过isalpha过滤非字母字符；

内容的提问来源于stack exchange，提问作者aidiotwholikescoding