C studing NO.18 函数练习

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<Windows.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>
//--------------
// 函数练习
//--------------

//练习一：写一个函数判断一个数是不是素数
int panduan(num1)
{
  int num2 = 0;
  for (int i = 2; i < num1 / 2; i++)
  {
    if (num1 % i == 0)
    {
      num2 = 1;
      return num2;
    }
  }
  num2 = 0;
  return num2;
}
int main()
{
  int a = 0;
  scanf("%d", &a);
  int b = panduan(a);
  if (1 == b)
  {
    printf("不是素数\n");
  }
  else
    printf("是素数\n");
  return 0;
}

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<Windows.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>
//---------------------------------
// 练习二、二分法求数组下标
//---------------------------------
int jisuan(int a[], int b, int c)
{
  int left = 0;
  int right = c - 1;
  while (left <= right)
  {
    int mid = (left + right) / 2;
    if ( a[mid] > b )
    {
      right = mid - 1;
    }
    else if (a[mid] < b)
    {
      left = mid + 1;
    }
    else
    {
      return mid;
    }
  }
  return -1;
}
int main()
{
  int arr[20] = { 1,2,3,4,5,6,7,8,9,10 };
  int sz = sizeof(arr) / sizeof(arr[0]);
  int k = 11;
  int ret = jisuan(arr, k, sz);
  if (-1 == ret)
  {
    printf("找不到");
  }
  else
  {
    printf("找到了，下标是 %d\n", ret);
  }

  return 0;
}