1
在下面的程序中，長度長於所需
int * accepted_ids = (int *) malloc(sizeof(int)*N);
double * accepted_scores = (double *)malloc(sizeof(double)*N);
int * unaccepted_ids = (int *) malloc(sizeof(int)*N);
double * unaccepted_scores = (double *) malloc(sizeof(double)*N);
這些內存分配所創建尺寸N陣列爲他們每個人，即使需要的元素的數量比的N低得多。
由於程序使用的是隨機數生成器，因此我們無法預先知道每個人需要多少內存。
我該如何解決這個困境？
（最多5分）
單個維度陣列SCORES商店 Ñ他們在高中獲得大學的候選得分。數組元素 的索引是這些候選人的ID。大學接受 申請，申請人的平均分數大於或等於 至4.0。編寫一個簡短的程序，會顯示：
•被接受的候選人與他們的身份證號碼和他們的平均得分列表。 •未被接受的候選人名單及其ID號碼和 平均分數 •接受和未接受的候選人人數。 •結果按排序 升序
平均得分應該用範圍< 2,6>使用隨機數發生器計算 。候選人總數 應作爲命令行參數傳遞給程序。 使您的程序對錯誤參數的輸入敏感。
不允許使用struct。
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <errno.h>
// This function tests whether it is possible
// to convert a string into integer or not.
//
// This function is needed to check the
// input argument otherwise if you type
// C:\>myapp.exe abc
// your program will crash.
int is_integer(const char * s)
{
char * endptr;
int radix = 10;//decimal number system
// try to convert s to integer
strtol(s, &endptr, radix);
errno = 0;
// if this conditions are fullfilled,
// that means, s can't be converted
// to an integer.
if (endptr == s || *endptr != '\0')
{
// argument must be an integer value
return 0; // failure
}
if (errno == ERANGE)
{
// int argument out of range
return 0; // failure
}
return 1; //success
}
// This function is needed to convert
// a string to an integer value.
int string_to_integer(const char * s)
{
char * endptr;
int radix = 10;//decimal number system
// convert s to integer
return strtol(s, &endptr, radix);
}
// Generte a random number between M and N.
//
// This function is needed coz rand() can
// generate only integer values.
double round_between_m_to_n(double M, double N)
{
return M + (rand()/(RAND_MAX/(N - M)));
}
// This is Bubble sort algorithm
// This is implemented as a user-defined function,
// coz, you have to use this twice.
// First for accepted scores,
// then for unaccepted scores.
void sort(int * ids, double * scores, int count)
{
for (int i = 0; i < count; i++)
{
for (int j = 0; j < i; j++)
{
if (scores[i] < scores[j])
{
// Swap scores
double temp = scores[i];
scores[i] = scores[j];
scores[j] = temp;
// Swap ids
int temp2 = ids[i];
ids[i] = ids[j];
ids[j] = temp2;
}
}
}
}
// This function is to print ids and scores
// as a table.
// This is implemented as a user-defined function,
// coz, you have to use this twice.
// First for accepted scores,
// then for unaccepted scores.
void print(int * ids, double * scores, int count)
{
printf("id\tavg_score\n");
printf("-------------------\n");
for (int i = 0; i < count; i++)
{
printf("%i\t%.1f\n", ids[i], scores[i]);
}
}
int main(int argc, char ** argv)
{
// Program can proceed only if
// the # of arguments is exactly 2.
// The 1st arg is always app-name.
if (argc != 2)
{
printf("insufficient argument\n");
return EXIT_FAILURE;
}
int N = 0;
int accepted_scores_count = 0;
int unaccepted_scores_count = 0;
double acceptance_threshhold = 4.0;
if (!is_integer(argv[1]))
{
printf("incorrect argument type\n");
return EXIT_FAILURE;
}
else
{
N = string_to_integer(argv[1]);
printf("Total %d students\n", N);
}
// Pair of variables are needed to
// keep track of student-ids.
// Otherwise, you can't tell what id a
// student has when data are sorted.
int * accepted_ids = (int *)malloc(sizeof(int)*N);
double * accepted_scores = (double *)malloc(sizeof(double)*N);
int * unaccepted_ids = (int *)malloc(sizeof(int)*N);
double * unaccepted_scores = (double *)malloc(sizeof(double)*N);
//Initialize random seed.
//If you don't use this, rand() will generate
//same values each time you run the program.
srand(time(NULL));
// Simultaneously generate scores, ids, and
// store them is sepaerate arrays.
for (int i = 0; i < N; i++)
{
int id = i;
double score = round_between_m_to_n(2, 6);
// if the score is greater than or
// equal to 4.0...
if (score >= acceptance_threshhold)
{
accepted_ids[accepted_scores_count] = i;
accepted_scores[accepted_scores_count] = score;
accepted_scores_count++;
}
// ... otherwise they are unaccepted.
else
{
unaccepted_ids[unaccepted_scores_count] = i;
unaccepted_scores[unaccepted_scores_count] = score;
unaccepted_scores_count++;
}
}
// sort accepted students
sort(accepted_ids, accepted_scores, accepted_scores_count);
// sort unaccpeted students
sort(unaccepted_ids, unaccepted_scores, unaccepted_scores_count);
// print accepted students
printf("\naccepted students\n");
print(accepted_ids, accepted_scores, accepted_scores_count);
// print unaccepted students
printf("\nunaccepted students\n");
print(unaccepted_ids, unaccepted_scores, unaccepted_scores_count);
printf("\nEnd of program.\n");
free(accepted_ids);
free(accepted_scores);
free(unaccepted_ids);
free(unaccepted_scores);
return EXIT_SUCCESS;
}
*「這些內存分配正在爲它們中的每一個創建大小爲N的數組，即使所需元素的數量遠遠低於N的數量。」您告訴程序要分配那麼多。如果你想減少，找出你需要多少，然後分配這個數額。 – InternetAussie
@InternetAussie，是的。那就是問題所在。由於該程序正在使用隨機數生成器，因此我們無法事先告訴每個人需要多少內存。 – anonymous
[不要投出'malloc'的結果]（http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc） – UnholySheep