#include<stdio.h>
int max(int a[],int len)
{
	int maxid=0;
	int i=1;
	for(;i<len;i++ )
	{
		if(a[i]>a[maxid])
		{
			maxid=i;
		}
	}
	return maxid; //return the subscript what represents the max number of a[]
}
int main()
{
   	int a[]={0,1,2,5,6,4,2,36,58,4,1,57,21};
   	int len=sizeof(a)/sizeof(a[0]);
   	int i=len-1;
   	for(;i>0;i--)
	{
	   	int	maxid=max(a,i+1);
	   	//swap a[maxid],a[len-1]
	   	int t=a[maxid];
	   	a[maxid]=a[i];
	    a[i]=t; // Swap the max number with the last subscript 
	} 
	int j=0;
	for(;j<len;j++)
	{
		printf("%d ",a[j]);
	 } 
//	printf("%d\n",maxid);
    return 0;
}
 

再看另一個沒有單獨寫出函式然後呼叫的，似乎前者更好理解：

#include<stdio.h>
int main(void)
{
	int i,index,j,n,temp;
	int a[10];
	printf("Enter n:");
	scanf("%d",&n);
	printf("Enter %d integers:",n);
	for(i=0;i<n;i++)
		scanf("%d",&a[i]);
	for(j=0;j<n-1;j++)	//why is it "n-1"? 
	//Because the value whose number is "n-1" will be decided without more sorting behaviour as the value whose number is "n-2" is on the right seat. 
	{
		index=j;	
		//At first, a[index] means a[0], so i=j+1; and secondly,a[index] means a[1]…
		for(i=j+1;i<n;i++)	
		//i=j+1 ensures that the last smaller value cannot be included in computing.To achive the goals of sorting.
			if(a[i]<a[index])	index=i;
		// If you want to sort this set of number by big to small, you just change "<" into ">".
		//To find the smallest value of the remaining values and swap it or not to take it to the right seat
		temp=a[index];	
		a[index]=a[j];
		a[j]=temp;
	}
	printf("After sorted:");
	for(i=0;i<n;i++)
	{
		printf("% d",a[i]);
	}
	return 0;
 }