C++ C 有没有办法比较多个字符串 [我通过fgets()输入它们]

代码中存在多个问题:

• fgets()存储目标数组末尾的尾随换行符，因此与单位字符串的所有比较都将失败.
• 您应该使用中间单元，以避免测试所有组合.

以下是修改后的版本:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct unit {
    double factor;
    const char *abbrev, *singular, *plural;
} const units[] = {
    { 1, "mm", "millimeter", "millimeters" },
    { 10, "cm", "centimeter", "centimeters" },
    { 100, "dm", "decimeter", "decimeters" },
    { 1000, "m", "meter", "meters" },
    { 10000, "dam", "decameter", "decameters" },
    { 100000, "hm", "hectometer", "hectometers" },
    { 1000000, "km", "kilometer", "kilometers" },
    { 25.4, "in", "inches", "inches" },
    { 304.8, "ft", "foot", "feet" },
    { 914.4, "yd", "yards", "yards" },
    { 201168, "fur", "furlong", "furlongs" },
    { 1609344, "mi", "mile", "miles" },
};

int get_unit(void) {
    char buf[40];
    while (fgets(buf, sizeof buf, stdin)) {
        buf[strcspn(buf, "\n")] = '\0';   // remove the newline if any
        for (int i = 0, n = sizeof(units) / sizeof(*units); i < n; i++) {
            if (!strcmp(buf, units[i].abbrev)
            ||  !strcmp(buf, units[i].singular)
            ||  !strcmp(buf, units[i].plural)) {
                return i;
            }
        }
        printf("unknown unit\n");
    }
    printf("unexpected end of file, aborting\n");
    exit(1);
}

int main(void) {
    int from, to;
    double val;

    printf("Enter what you want to convert from: ");
    from = get_unit();

    printf("Enter what you want to convert to: ");
    to = get_unit();

    printf("Enter the numerical value of conversion: ");
    if (scanf("%lf", &val) == 1) {
        double result = val * units[from].factor / units[to].factor;
        printf("Answer is %g %s\n", result, result == 1 ? units[to].singular : units[to].plural);
        return 0;
    }
    return 1;
}