1 全局变量和局部变量初始值
局部变量不加static关键字就是错误的
2 输入数字求平均值
#include <stdio.h>int main()
{int t;double sum = 0;int cnt = 0;scanf_s("%d",&t);while (t != -1 ){printf("第%d个，%d\r\n",cnt, t);sum += t;cnt++;scanf_s("%d",&t);}if (cnt > 0){printf("%f\n",sum/cnt);}return 0;
}
3 定义数组
1 数组定义
2 数组的大小的计算
3 数组之意事项
#include <stdio.h>int main()
{int t;double sum = 0;int cnt = 0;int number[100];scanf_s("%d",&t);while (t != -1 ){number[cnt] = t;{int i;printf("%d\t", cnt);for (i = 0; i <= cnt; i++){printf("%d\t", number[i]);}printf("\n");}sum += t;cnt++;scanf_s("%d",&t);}if (cnt > 0){printf("%f\n", sum / cnt);int i;for ( i = 0; i < cnt; i++){double div = sum / cnt;if (number[i] > div){printf("%d\n", number[i]); }}}return 0;
} 
4 写一个程序，输入数量不确定的[0,9]范围内的整数，统计每一种数字出现的次数，输入-1表示结束
#include <stdio.h>int main() {int num;int counts[10] = { 0 }; // 用于存储 0-9 每个数字出现的次数printf("请输入[0,9]范围内的整数，输入 -1 表示结束。\n");while (1) {scanf_s("%d", &num);if (num == -1) {break;}if (num >= 0 && num <= 9) {counts[num]++;}else {printf("输入错误，请重新输入[0,9]范围内的整数或 -1 结束。\n");}}for (int i = 0; i < 10; i++) {if (counts[i] > 0) {printf("数字 %d 出现了 %d 次。\n", i, counts[i]);}}return 0;
} 