用c语言写归并排序18，2，20，34，12，32，6，16

好的，下面是使用C语言编写归并排序的代码：

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

void merge(int arr[], int left, int mid, int right) {
    int i, j, k;
    
    int n1 = mid - left + 1;
    int n2 = right - mid;
    
    int *L = (int*)malloc(sizeof(int) * n1);
    int *R = (int*)malloc(sizeof(int) * n2);
    
    for(i = 0; i < n1; i++)
        L[i] = arr[left + i];
    for(j = 0; j < n2; j++)
        R[j] = arr[mid + 1 + j];
    
    i = 0;
    j = 0;
    k = left;
    while(i < n1 && j < n2) {
        if(L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
    
    while(i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
    
    while(j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
    
    free(L);
    free(R);
}

void mergeSort(int arr[], int left, int right) {
    if(left < right) {
        int mid = left + (right - left) / 2;
        
        mergeSort(arr, left, mid);
        mergeSort(arr, mid + 1, right);
        
        merge(arr, left, mid, right);
    }
}

int main() {
    int arr[] = {18, 2, 20, 34, 12, 32, 6, 16};
    int n = sizeof(arr) / sizeof(arr[0]);
    
    printf("Before Sorting:\n");
    for(int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");
    
    mergeSort(arr, 0, n - 1);
    
    printf("After Sorting:\n");
    for(int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");
    
    return 0;
}

输出结果为：

Before Sorting:
18 2 20 34 12 32 6 16 
After Sorting:
2 6 12 16 18 20 32 34 

希望我的回答对您有所帮助！