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15.
#include<stdio.h>
#include<string.h>
int main()
{
char arr1[] = "welcome to beijing!!!!";
char arr2[] = "######################";
int left = 0;
//int right = sizeof(arr1) / sizeof(arr1[0]) - 2;
int right = strlen(arr1)-1;
while (left<=right)
{
?? ?arr2[left] = arr1[left];
?? ?arr2[right] = arr1[right];
?? ?printf("%s\n", arr2);
?? ?left++;
?? ?right--;
}
return 0;
}
16.
#include<stdio.h>
int main()
{
?? ?int arr[] = { 1,2,3,4,5,6,7,8,9,10 };//下标 [0,1,2,3,4,5,6,7,8,9]
?? ?int k = 9;
?? ?int left = 0;//左下标
?? ?int sz = sizeof(arr) / sizeof(arr[0]);
?? ?int right = sz - 1;//右下标
?? ?int mid = (left + right) / 2;
?? ?while (left<=right)
?? ?{
?? ??? ?int mid = (left + right) / 2;
?? ??? ?if (arr[mid] > k)
?? ??? ?{
?? ??? ??? ?right = mid - 1;//右边向左靠
?? ??? ?}
?? ??? ?else if (arr[mid] < k)
?? ??? ?{
?? ??? ??? ?left = mid + 1;//左边像右靠
?? ??? ?}
?? ??? ?else
?? ??? ?{
?? ??? ??? ?printf("找到了，下标是:%d\n", mid);
?? ??? ??? ?break;
?? ??? ?}
?? ?}
?? ?if (left>right)
?? ?{
?? ??? ?printf("找不到了\n");
?? ?}
?? ?return 0;
}
17.
#include<stdio.h>
int main()
{
?? ?int ?arr[] = { 1,2,3,4,5,6,7,8,9,10 };
?? ?int i = 0;
?? ?int k = 7;
?? ?int sz = sizeof(arr) / sizeof(arr[0]);
?? ?for (int i = 0; i < sz; i++)
?? ?{
?? ??? ?if (k == arr[i])
?? ??? ?{
?? ??? ??? ?printf("找到了,下标是：%d\n", i);
?? ??? ??? ?break;
?? ??? ?}
?? ?}
?? ?if (i == sz)
?? ?{
?? ??? ?printf("找不到\n");
?? ?}
?? ?return 0;
}
18.
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<Windows.h>
int main()
{
?? ?int i = 0;
?? ?char password[20] = { 0 };
?? ?for ( ?i = 0; ?i <=3; ?i++)
?? ?{
?? ??? ?printf("请输入密码:");
?? ??? ?scanf_s("%s", &password);
?? ??? ?if (strcmp(password,"123456")==0)
?? ??? ?{
?? ??? ??? ?printf("登录成功\n");
?? ??? ??? ?break;
?? ??? ?}
?? ??? ?else
?? ??? ?{
?? ??? ??? ?printf("密码错误\n");
?? ??? ?}
?? ?}
?? ?if (i == 3)
?? ?{
?? ??? ?printf("三次密码均错误，程序已退出\n");
?? ?}
return 0;
}
19.
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main()
{
?? ?int num = rand() % 100 + 1;
?? ?int count = 0; ?//用的次数
?? ?int a = 0; ? //输入的值
?? ?printf("我已经想好0-100之间的数");
?? ?do {
?? ??? ?scanf_s("%d", &a);
?? ??? ?if (a > num) {
?? ??? ??? ?printf("你的值偏大了，再试试吧。");
?? ??? ?}else if(a<num){
?? ??? ??? ?printf("你的值偏小了再试试吧。");
?? ??? ?}
?? ??? ??? ??? ?count++;
?? ?} while (a != num);
?? ?printf("恭喜你答对了%d,用了%d次", num,count);?
?? ??? ?return 0;
}
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