C语言及程序设计提高例程-27 编写查找和排序函数

贺老师教学链接  C语言及程序设计提高 本课讲解

用函数实现二分查找

#include <stdio.h>
int binary_search(int arr[], int n, int k);
#define SIZE 10
int main( )
{
    int d[SIZE] = {1, 3, 9, 12, 32, 41, 45, 62, 75, 77};
    int low, high,mid,key,index=-1;
    printf("Input a key you want to search: ");
    scanf("%d" , &key);
    index = binary_search(d, SIZE, key);
    if(index >= 0)
        printf("The index of the key is %d .\n", index);
    else
        printf("Not found.\n");
    return 0;
}
/*
功能：在长度为n的有序数组中查找k出现的位置
*/
int binary_search(int arr[], int n, int k)
{
    int i=-1;
    int low=0,high=n-1,mid;
    while(low<=high)
    {
        mid=(low+high)/2;
        if(arr[mid]==k)
        {
            i=mid;
            break;
        }
        else if(arr[mid]>k)
            high=mid-1;
        else
            low=mid+1;
    }
    return i;
}

用函数实现选择法算法

#include <stdio.h>
int main( )
{
    void select_sort(int array[],int n);             //函数声明
    int a[10]= {4,3,7,9,1,5,0,8,2,6},i;
    select_sort(a,10);                              //函数调用，数组名作实参
    printf("the sorted array：\n");
    for(i=0; i<10; i++)                             //输出10个已排好序的数
        printf("%d ", a[i]);
    printf("\n");
    return 0;
}

void select_sort(int array[],int n)              //形参array是数组名
{
    int i,j,k,t;
    for(i=0; i<n-1; i++)
    {
        k=i;  //先设第i个就为最小
        for(j=i+1; j<n; j++)
            if(array[j]<array[k])
                k=j;   //通过循环，得到k为最小
        t=array[k];    //交换a[i]和a[k]
        array[k]=array[i];
        array[i]=t;
    }
    return;
}