输出：char* output，排好序之后的元音字符串

C代码如下：

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

int cmp(const void* a, const void* b);
int is_vowel(char a);
void sort_vowel(char* input, char* output);

int main()
{
	char input[1000] = {'\0'};
	char output[200] = {'\0'};

	printf("please input the original str: ");
	gets(input);

	printf("the sorted vowel is: ");
	sort_vowel(input,output);
	return 0;
}

int cmp(const void* a, const void* b)
{
	return *(char*)a - *(char*)b;
}

int is_vowel(char a)
{
	if(a=='a' || a=='e' || a=='i' || a=='o' || a=='u' ||
		a=='A' || a=='E' || a=='I' || a=='O' || a=='U')
		return 1;
	else
		return 0;
}

void sort_vowel(char* input, char* output)
{
	char low[100] = {'\0'};
	char up[100] ={'\0'};
	int low_index=0;
	int up_index=0;
	while(*input != '\0')
	{
		if(is_vowel(*input))
		{
			if(isupper(*input))
			{
				up[up_index++] = *input;
				input++;
				continue;
			}
			else
			{
				low[low_index++] = *input;
				input++;
				continue;
			}
		}
		input++;
	}
	qsort(up,strlen(up),sizeof(char),cmp);
	qsort(low,strlen(low),sizeof(char),cmp);
	strcat(low,up);
	strcpy(output,low);
	while(*output != '\0')
		printf("%c",*output++);
	printf("\n");
}