用C语言输入一行字符，统计英文字母、空格、数字和其他字符的个数。

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

int main() {
    char str[100];
    int letters = 0, spaces = 0, digits = 0, others = 0;
    printf("Please input a string: ");
    fgets(str, sizeof(str), stdin);

    for (int i = 0; str[i] != '\0'; i++) {
        if (isalpha(str[i])) {
            letters++;
        } else if (isspace(str[i])) {
            spaces++;
        } else if (isdigit(str[i])) {
            digits++;
        } else {
            others++;
        }
    }

    printf("Number of letters: %d\n", letters);
    printf("Number of spaces: %d\n", spaces);
    printf("Number of digits: %d\n", digits);
    printf("Number of other characters: %d\n", others);
    return 0;
}