C2106 : '=' : left operand must be l-value

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所以，我正在学习 C 作为我的第一语言，并且在进行一些编码练习时，我遇到了上述错误。我按照书上所说的做了一切(Stephen G. Kochan:C 语言编程，第三版)。我究竟做错了什么？我使用的是 Microsoft Visual Studio 2015。

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struct date
{
int month;
int day;
int year;
};

int main(void)
{
    struct date today, tomorrow;
    int numberOfDays(struct date d);

    printf("Adja meg a mai datumot (hh nn eeee): ");
    scanf_s("%i%i%i", &today.month, &today.day, &today.year);

    if (today.day != numberOfDays(today))
    {
        tomorrow.day = today.day + 1;
        tomorrow.month = today.month;
        tomorrow.year = today.year;
    }
    else if (today.month == 12)
    {
        tomorrow.day = 1;
        tomorrow.month = 1;
        tomorrow.year = today.year + 1;
    }
    else
    {
        tomorrow.day = 1;
        tomorrow.month = today.month + 1;
        tomorrow.year = today.year;
    }
    printf("A holnapi datum: %i/%i/%.2i.\n", tomorrow.month, tomorrow.day, tomorrow.year % 100);

    return 0;
}

int numberOfDays(struct date d)
{
    int days;
    bool isLeapYear(struct date d);
    const int daysPerMonth[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

    if (isLeapYear(d) == true && d.month == 2)
        days = 29;
    else
        days = daysPerMonth[d.month - 1];

    return days;
}

bool isLeapYear(struct date d)
{
    bool leapYearFlag;

    if ( (d.year % 4 == 0 && d.year % 100 = 0) || d.year % 400 == 00) //The error shows up here
        leapYearFlag = true;
    else
        leapYearFlag = false;

    return leapYearFlag;
}

Answer 1

这里有一个错别字

if ( (d.year % 4 == 0 && d.year % 100 = 0) || d.year % 400 == 00) 
                                    ^^^^

我想你的意思是

if ( (d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 00) 
                                     ^^^^

00 相当于 0.:)

函数可以写得更简单

bool isLeapYear( struct date d )
{
    return ( d.year % 4 == 0 && d.year % 100 != 0 ) || ( d.year % 400 == 0 );
}