c - 检查文件中最常见的字母时如何忽略 ctrl+z(不区分大小写)

Question

该函数需要查找文件中最常见的字符，并从用户那里获取数据。我使用 ctrl+z 来终止。

问题是当我输入大字符时，例如:A + ctrl+Z，那么它会将Z视为最常见的字符。(如果字符数量相同，则按字母顺序返回最大的。空文件将返回'\0')。

char commonestLetter(){
    char ch;
    int count[26] = {0}, max = 0, index, i;
    FILE* f = fopen("input.txt","w");
    if (f == NULL){
        printf("Failed to open the file \n");
        return;
    }
    printf("Please enter the characters one by one, followed by enter\n");
    printf("Ctrl + z and enter to finish\n");
    while((ch = getchar()) != EOF){
        fprintf(f,"%c",ch);
        _flushall();
        if (isalpha(ch))
            count[ch - 'a']++;
    }
    fseek(f, 0, SEEK_END);
    if (ftell(f) == 0){
        ch = '\0';
        return ch;
    }
    for (i = 0; i < 26; i++){
        if (count[i] >= max){
            max = count[i];
            index = i;
        }
    }
    fclose(f);
    return index + 'A';
}

int main(){
    char ch;
    ch = commonestLetter();
    if(ch)
        printf("The commonest letter is %c", ch);
    else
        printf("No letters in the file");
    printf("\n");
    system("pause"); 
    return 0;   
}

Answer 1

1. 您声明该函数应该在文件中查找最常见的字母，但您从标准输入中读取字母。
2. 要获得最常见的字母忽略大小写，您必须使用字母提升函数，例如 tolower()。

试试这个:

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

char commonestLetter(char *file_name)
{
    char ch, max_char = '\0';
    int count[26] = {0}, max_count = 0;

    FILE *f = fopen(file_name, "r");
    if (f == NULL) {
        printf("Failed to open the file %s\n", file_name);
        return '\0';
    }

    while (fread(&ch, 1, 1, f) > 0) {
        if (isalpha(ch) &&
            (++count[tolower(ch) - 'a']) > max_count)
            max_char = ch;
    }
    fclose(f);
    return max_char;
}

int main(int argv, char *argc[])
{
    char ch;
    if (argv < 2) {
        printf("Usage: %s filename\n", argc[0]);
        exit();
    }

    ch = commonestLetter(argc[1]);
    if(ch)
        printf("The commonest letter in the file %s is '%c'\n",
               argc[1], ch);
    else
        printf("No letters in the file %s\n", argc[1]);

    return 0;   
}