C 编程：使用结构和函数确定两个日期之间的天数

Question

我已经做出了 Craig Estey 建议的更正。 代码现在可以编译并运行。 这是修改后的代码：

/* Programme to determine the number of days between two dates ex8.2.c
This is done with the formula
N = ( ((1461 * (f(year, month))) / 4) + ((153 * (g(month))) / 5) + day )

with:
f(year, month) = year - 1 if month <= 2; otherwise year

g(month) = month + 13 if month <=2; otherwise month + 1

The formula is applicable for dates after 1 March 1900;
    add 1 to N for dates between 1 March 1800 to 28 February 1900
    add 2 to N for dates between 1 March 1700 to 28 February 1800

ALGORITHMS
N.B.: Use ternary operators to help with different evaluations

Declare structure(s) to store date
Write functions to evaluate f
Write function to evaluate g
Compare date periods to know if modification of formula will be used

 */

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

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

struct date date1, date2;
int month, year, duration1, duration2, diff;

// Function prototypes
int number_of_Days (struct date d);
bool is_Leap_Year (struct date d);
int year_Func (int month, int year);
int month_Func (int month);
int date_Elapsed (struct date d);

int main(void)
{
    printf("This is a programme to find the number of days between two dates!\n");

    printf("\nEnter first date (dd mm yyyy): ");
    scanf(" %i%i%i", &date1.day, &date1.month, &date1.year);
        month = date1.month;
        year = date1.year;

    duration1 = date_Elapsed (date1);

    printf("\nEnter second date (dd mm yyyy): ");
    scanf(" %i%i%i", &date2.day, &date2.month, &date2.year);
        month = date2.month;
        year = date2.year;

    duration2 = date_Elapsed (date2);

    diff = duration2 - duration1;

    printf("Number of elapsed days are: %i.\n", diff);
}

// Function to find the number of days in a month
int number_of_Days (struct date d)
{
    int days;
    bool is_Leap_Year (struct date d);
    const int days_Per_Month[13] = {0, 31, 28, 31, 30, 31, 30,
                                        31, 31, 30, 31, 30, 31};

    if (is_Leap_Year (d) == true && d.month == 2)
    {
        days = 29;
    }
    else
    {
        days = days_Per_Month[d.month];
    }
    return days;
}

// Function to determine if it is a leap year
bool is_Leap_Year (struct date d)
{
    bool leap_Year_Flag;

    if ((d.year % 4 == 0 && d.year % 100 != 0) || (d.year % 400 == 0))
    {
        leap_Year_Flag = true;
    }
    else
    {
        leap_Year_Flag = false;
    }
    return leap_Year_Flag;
}

// Function to find f in formula
int year_Func (int month, int year)
{
    int yrRet;
    yrRet = (month <= 2) ? (year - 1) : (year);
    return yrRet;
}

// Function to find g in formula
int month_Func (int month)
{
    int mntRet;
    mntRet = (month <= 2) ? (month + 13) : (month + 1);
    return mntRet;
}

// Function to calculate N in formula
int date_Elapsed (struct date d)
{
    int number_of_Days (struct date d);
    bool is_Leap_Year (struct date d);
    int year_Func (int month, int year);
    int month_Func (int month);

    int yCalc, mCalc, nCalc;

    yCalc = year_Func (d.month, d.year);
    mCalc = month_Func (d.month);

    // Calculates number of elapsed days
    nCalc = ( ((1461 * (yCalc) / 4) + ((153 * (mCalc))) / 5) + d.day );

    if ((d.day < 1) && (d.month < 3) && (d.year < 1700))
    {
        printf("Invalid date input!\n");
        printf("Date must be from 1 March 1700.\n");
        exit (999);
    }
    else if (((d.day >= 1) && (d.month >= 3) && (d.year >= 1700)) && ((d.day <= 28) && (d.month <= 2) && (d.year <= 1800)))
    {
        nCalc = nCalc + 2;
    }
    else if (((d.day >= 1) && (d.month >= 3) && (d.year >= 1800)) && ((d.day <= 28) && (d.month <= 2) && (d.year <= 1900)))
    {
        nCalc = nCalc + 1;
    }
    else
    {
        return nCalc;
    }
}

================================================== ==============================

我是一个学习计算机编程的新手。 这是 Stephen G. Kochan 的 Programming in C 练习。 到目前为止，我需要帮助来查明错误。 我已经坚持了大约一个星期。

我的 Code::Blocks 编译器显示以下错误：

||=== Build file: "no target" in "no project" (compiler: unknown) ===|
|In function ‘N’:|
|134|error: lvalue required as left operand of assignment|
|144|error: lvalue required as left operand of assignment|
|148|error: lvalue required as left operand of assignment|
|152|warning: return makes integer from pointer without a cast [-Wint-conversion]|
|154|warning: control reaches end of non-void function [-Wreturn-type]|
||=== Build failed: 3 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

这是我的代码

/* Programme to determine the number of days between two dates ex8.2.c
This is done with the formula
N = ( ((1461 * (f(year, month))) / 4) + ((153 * (g(month))) / 5) + day )

with:
f(year, month) = year - 1 if month <= 2; otherwise year

g(month) = month + 13 if month <=2; otherwise month + 1

The formula is applicable for dates after 1 March 1900;
    add 1 to N for dates between 1 March 1800 to 28 February 1900
    add 2 to N for dates between 1 March 1700 to 28 February 1800

ALGORITHMS
N.B.: Use ternary operators to help with different evaluations

Declare structure(s) to store date
Write functions to evaluate f
Write function to evaluate g
Compare date periods to know if modification of formula will be used

*/

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

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

struct date date1, date2;
int month, year, N1, N2, diff;

// Function prototypes
int number_of_Days (struct date d);
bool is_Leap_Year (struct date d);
int F (int month, int year);
int G (int month);
int N (struct date d);

int main(void)
{
    //
    printf("This is a programme to find the number of days between two dates!\n");

    printf("\nEnter first date (dd mm yyyy): ");
    scanf(" %i%i%i", &date1.day, &date1.month, &date1.year);
        month = date1.month;
        year = date1.year;

    N1 = N (date1);

    printf("\nEnter second date (dd mm yyyy): ");
    scanf(" %i%i%i", &date2.day, &date2.month, &date2.year);
        month = date2.month;
        year = date2.year;

    N2 = N (date2);

    diff = N2 - N1;

    printf("Number of elapsed days are: %i.\n", diff);
}

// Function to find the number of days in a month
int number_of_Days (struct date d)
{
    int days;
    bool is_Leap_Year (struct date d);
    const int days_Per_Month[13] = {0, 31, 28, 31, 30, 31, 30,
                                        31, 31, 30, 31, 30, 31};

    if (is_Leap_Year (d) == true && d.month == 2)
    {
        days = 29;
    }
    else
    {
        days = days_Per_Month[d.month];
    }
    return days;
}

// Function to determine if it is a leap year
bool is_Leap_Year (struct date d)
{
    bool leap_Year_Flag;

    if ((d.year % 4 == 0 && d.year % 100 != 0) || (d.year % 400 == 0))
    {
        leap_Year_Flag = true;
    }
    else
    {
        leap_Year_Flag = false;
    }
    return leap_Year_Flag;
}

// Function to find f
int F (int month, int year)
{
    int F;
    F = (month <= 2) ? (year - 1) : (year);
    return F;
}

// Function to find g
int G (int month)
{
    int G;
    G = (month <= 2) ? (month + 13) : (month + 1);
    return G;
}

// Function to calculate N
int N (struct date d)
{
    int number_of_Days (struct date d);
    bool is_Leap_Year (struct date d);
    int F (int month, int year);
    int G (int month);

    int f, g;

    f = F (d.month, d.year);
    g = G (d.month);

    //N = ( ((1461 * (f(d.month, d.year))) / 4) + ((153 * (g(d.month))) / 5) + d.day );
    N = ( ((1461 * (f) / 4) + ((153 * (g))) / 5) + d.day );

    if ((d.day < 1) && (d.month < 3) && (d.year < 1700))
    {
        printf("Invalid date input!\n");
        printf("Date must be from 1 March 1700.\n");
        exit (999);
    }
    else if (((d.day >= 1) && (d.month >= 3) && (d.year >= 1700)) && ((d.day <= 28) && (d.month <= 2) && (d.year <= 1800)))
    {
        N = N + 2;
    }
    else if (((d.day >= 1) && (d.month >= 3) && (d.year >= 1800)) && ((d.day <= 28) && (d.month <= 2) && (d.year <= 1900)))
    {
        N = N + 1;
    }
    else
    {
        return N;
    }
}

Answer 1

违规行是：

N = (((1461 * (f) / 4) + ((153 * (g))) / 5) + d.day);

但是，这是在函数N内部。

您不能分配给函数名称。

更改函数名称（例如N --> Ncalc ）或为保存返回值的变量使用不同的名称（例如ret ）。

分配给N其中N是包含函数是fortran [IIRC] 中用于设置函数返回值的事情。 这在c不太好用。

而且，您必须提供变量的定义（例如）：

int ret;

---

一些风格的项目...

按照惯例，在c ，使用所有大写字母通常是为常量保留的（例如）：

#define X 12345

尽管按值传递struct是完全合法的，但大多数代码会传递一个指向结构体的指针（可能使用const ），因为它更快。

int
N(struct date *d)
{
}

想象一下，如果您的struct是：

struct date {
    ...
    int array[10000];
};

它会将大约 40,000 个字节推入堆栈。

此外，使用 [更长] 比单字符名称更具描述性的名称也很有帮助。 您有函数来“计算” f 、 g和n命名为F 、 G和N 。

那么，什么是 [an] f [或g或n ]？？？ 任何[其他] 阅读你的代码的人都会想知道。

使用更具描述性的注释，相当于：

// set x to the value of 10
x = 10;