C语言第25天，练习题，杨辉三角

unsigned

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	unsigned char a = 200;//无符整型
	unsigned char b = 100;
	unsigned char c = 0;
	c = a + b;//整型提升
	printf("%d %d", a + b, c);//300,44
} 

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	unsigned int a = 0x1234;
	unsigned char b = *(unsigned char*)&a;
	printf("%d\n", b);//52
	return 0;
}

字符长度问题

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <string.h>

int main() {
	char a[1000] = { 0 };
	int i = 0;
	for (i = 0; i < 1000; i++) {
		a[i] = -1 - i;
	}
	//-1 -2 .... -128 127 126 ... 1
	printf("%d\n", strlen(a));//255

	return 0;
}

杨辉三角

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

//杨辉三角

int main() {
	int arr[10][10] = { 0 };
	int i = 0;
	int j = 0;
	for (i = 0; i < 10; i++) {
		for (j = 0; j < 10; j++) {

			if (j == 0) {
				arr[i][j] = 1;
			}
			if (i == j) {
				arr[i][j] = 1;
			}
			if (i >= 2 && j >= 1) {
				arr[i][j] = arr[i - 1][j] + arr[i - 1][j - 1];
			}
		}
	}
	//打印
	for (i = 0; i < 10; i++) {
		for (j = 0; j < 9 - i; j++) {
			printf(" ");
		}
		for (j = 0; j <= i; j++) {
			printf("%d ", arr[i][j]);
		}
		printf("\n");
	}
}

         1
        1 1
       1 2 1
      1 3 3 1
     1 4 6 4 1
    1 5 10 10 5 1
   1 6 15 20 15 6 1
  1 7 21 35 35 21 7 1
 1 8 28 56 70 56 28 8 1
1 9 36 84 126 126 84 36 9 1

指针难题

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	int a[5] = { 5,4,3,2,1 };
	int* ptr = (int*)(&a + 1);
	printf("%d,%d", *(a + 1), *(ptr - 1));//4,1
	//ptr - 数组地址的后一位
	//a+1 - a为首元素，a+1为第二个元素4
	//ptr-1 - 元素1的地址
	return 0;
}

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	int aa[2][5] = { 10,9,8,7,6,5,4,3,2,1 };
	int* ptr1 = (int*)(&aa + 1);
	int* ptr2 = (int*)(*(aa + 1));
	//aa是首元素地址-即第一行的地址,
	//aa+1是第二行的地址
	//ptr2是第二行第一列的元素 5 的地址
	printf("%d,%d", *(ptr1 - 1), *(ptr2 - 1));//1,6
	//ptr2-1是元素5向前一位，即元素 6 的地址
	return 0;
}