Task:

From the keyboard, enter a sequence of records with information about the capitals of European states: , , , . A public holiday date is specified as a character string in the form Day of the Month, for example August 24. Then rearrange the data in calendar order according to the dates of the main public holiday.

Attempt:

The code below is a bit complex and long, I would like to either split it into functions or replace it altogether with something simpler

const char *months[MONTHS_NUM] = {
    "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct",
    "nov", "dec"
};

typedef struct capital {
    char name[20];
    long int population;
    char holiday[60];
    char date[15];
} CAPITAL;

void
Sort_by_Date(CAPITAL arr[], int nc)
{
    int i, j;
    CAPITAL temp;
    int day1, day2;
    char month1[4], month2[4];
    int month1_idx, month2_idx;

    for (i = 0; i < nc - 1; i  ) {
        for (j = i   1; j < nc; j  ) {
            sscanf(arr[i].date, "%d %3s", &day1, month1);
            sscanf(arr[j].date, "%d %3s", &day2, month2);
            for (month1_idx = 0; month1_idx < MONTHS_NUM; month1_idx  ) {
                if (strcmp(months[month1_idx], month1) == 0)
                    break;
            }
            for (month2_idx = 0; month2_idx < MONTHS_NUM; month2_idx  ) {
                if (strcmp(months[month2_idx], month2) == 0)
                    break;
            }
            if (month1_idx != month2_idx)
                return month1_idx < month2_idx;
            else if (day1 != day2)
                return day1 < day2;
            if (month1_idx > month2_idx) {
                temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
            else if (month1_idx == month2_idx) {
                if (day1 > day1) {
                    temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
            }
        }
    }
}

CodePudding user response：

A few issues ...

1. Sort_by_Date should sort the entire array.
2. It loops on all dates, but it does a return on a mismatch.
3. The latter is what a sort comparison function should do.
4. The function also tries to swap out of order elements. That is what a sort function would do.
5. We need to split up the function into a sort function (similar to qsort) and a comparison function (similar/compatible with the last arg of qsort).
6. The compare function has to compare two keys: The month index and then the day value.
7. There is replicated code for decoding a date into a month index. This should be a separate function.

Here is a refactored version. It is annotated.

It has two versions of the sort function:

1. A wrapper around qsort
2. Original sort function cleaned up.

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

#define MONTHS_NUM      12

const char *months[MONTHS_NUM] = {
    "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct",
    "nov", "dec"
};

typedef struct capital {
    char name[20];
    long int population;
    char holiday[60];
    char date[15];
} CAPITAL;

// date_sort_key -- convert date into single/combined sort key
// RETURNS: mon|day
int
date_sort_key(const char *date)
{
    int monidx = -1;
    int day;
    char mon[10];

    // split date into day/month
    sscanf(date,"%d %3s",&day,mon);

    // convert month string into an index of (0-11)
    for (int idx = 0;  idx < MONTHS_NUM;    idx) {
        if (strcmp(months[idx],mon) == 0) {
            monidx = idx;
            break;
        }
    }

    // fail if month string is invalid
    if (monidx < 0) {
        fprintf(stderr,"date_sort_key: invalid month -- '%s'\n",mon);
        exit(1);
    }

    // get combined key of: mon|day
    monidx <<= 8;
    monidx |= day;

    return monidx;
}

// compare_dates -- qsort compatible compare function
int
compare_dates(const void *vlhs,const void *vrhs)
{
    const CAPITAL *lhs = vlhs;
    int lhsidx = date_sort_key(lhs->date);

    const CAPITAL *rhs = vrhs;
    int rhsidx = date_sort_key(rhs->date);

    // compare the two date keys
    int cmp = rhsidx - lhsidx;

    return cmp;
}

void
Sort_by_Date_qsort(CAPITAL arr[], int nc)
{

    qsort(arr,nc,sizeof(CAPITAL),compare_dates);
}

void
Sort_by_Date(CAPITAL arr[], int nc)
{
    int i, j;
    CAPITAL temp;

    for (i = 0; i < nc - 1; i  ) {
        for (j = i   1; j < nc; j  ) {
            int cmp = compare_dates(&arr[i],&arr[j]);
            if (cmp > 0) {
                temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }
}

CodePudding user response：

At least this problem:

Compare error

        if (month1_idx != month2_idx)
            return month1_idx < month2_idx;
        else if (day1 != day2)
            return day1 < day2;

        // This is never true as prior test is `month1_idx != month2_idx`
        if (month1_idx > month2_idx) {
            temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
        ...
           if (day1 > day1) {  // This is never true.  Looks like a typo.

Instead:

        // If greater than ... 
        int gt = month1_idx > month2_idx || (month1_idx == month2_idx && day1 > day2);
        if (gt) {
          // swap
          ...
        }