Question

/* C program for merge sort */

#include stdlib.h 
#include stdio.h

/* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */

void merge(int arr[], int l, int m, int r)

{

 int i, j, k;

    int n1 = m - l + 1;

    int n2 =  r - m;

    /* create temp arrays */
    int L[n1], R[n2];

    /* Copy data to temp arrays L[] and R[] */
    for(i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for(j = 0; j <= n2; j++)
        R[j] = arr[m + 1+ j];

    /* Merge the temp arrays back into arr[l..r]*/
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2)
    {
        if (L[i] <= R[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    /* Copy the remaining elements of L[], if there are any */
    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }

    /* Copy the remaining elements of R[], if there are any */
    while (j < n2)
    {
        arr[k] = R[j];
        j++;
        k++;
    }
}

/* l is for left index and r is right index of the sub-array

  of arr to be sorted */

void mergeSort(int arr[], int l, int r)
{

    if (l < r)
    {
        int m = l+(r-l)/2; //Same as (l+r)/2, but avoids overflow for large l and h
        mergeSort(arr, l, m);
        mergeSort(arr, m+1, r);
        merge(arr, l, m, r);
    }
}


/* UITLITY FUNCTIONS */


/* Function to print an array */

void printArray(int A[], int size)
{

    int i;
    for (i=0; i < size; i++)
        printf("%d ", A[i]);
    printf("\n");
}


/* Driver program to test above functions */

int main()
{

    int arr[] = {12, 11, 13, 5, 6, 7};
    int arr_size = sizeof(arr)/sizeof(arr[0]);

    printf("Given array is \n");
    printArray(arr, arr_size);

    mergeSort(arr, 0, arr_size - 1);

    printf("\nSorted array is \n");
    printArray(arr, arr_size);
    return 0;
}

Answer 1

您可能没有使用C99编译器，因此您尝试使用variable-length arrays无法编译。

Answer 2

您的标题应为

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

代码工作正常：http://ideone.com/YvnU4f。

请注意，代码是在C99模式下编译的，否则无法编译（因为在C99和后者中允许使用VLA）。使用-std=C99以C99模式编译它。

运行此程序时，常量表达式需要错误

2 个答案: