又又又一个没有意义的标题

1 折半查找

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
int main() {
	int a[10] = { 1,2,3,4,5,6,7,8,9,10 };
	int left=0, right=9, mid=0;
	int b;
	printf("输入你想查找的数字：\n");
	scanf("%d", &b);
	while (left < right) {
		mid = (left + right) / 2;
		if (b<a[mid]) {
			right = mid - 1;
		}
		else if (b>a[mid]) {
			left = mid + 1;
		}
		else {
			printf("%d\n", mid);
			break;
		}
	}
	if (left >= right) {
		printf("没有这个数字！\n");
	}
	system("pause");
	return 0;
}

2 输入密码

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main() {
	char a[20] = "bigbig";
	char b[20] = "";
	int i = 0;
	for ( i = 0; i < 3; i++) {
		printf("请输入你的密码：\n");
		scanf("%s", b);
		if (strcmp(a, b) == 0) {
			printf("输入正确！\n");
			break;
		}
	}
	if (i == 3) {
		printf("退出输入！\n");
	}
	system("pause");
	return 0;
}

3

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
int main() {
	char a;
	
	while(1) {
		a = getchar();
		if (a == '@') {
			break;
		}
		if (a<'z'&&a>'a') {
			putchar( a - 32);
		}
		else if (a<'Z'&&a>'A') {
			putchar( a + 32);
		}
		else {
			putchar(a);
		}
	}
	system("pause");
	return 0;
}