#include <stdio.h>

int main(){
	// 第一个C语言程序
	printf("hello world\n");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>

int main()
{
	//system("calc"); //windows平台
	system("ls"); //Linux平台, 需要头文件#include <stdlib.h>

	return 0;
}

#include <stdio.h>

int main()
{
	//定义整型变量a, b, c
	int a;
	int b;
	int c;

	__asm
	{
		mov a, 3	//3的值放在a对应内存的位置
		mov b, 4	//4的值放在b对应内存的位置
		mov eax, a	//把a内存的值放在eax寄存器
		add eax, b	//eax和b相加，结果放在eax
		mov c, eax	//eax的值放在c中
	}
	
	printf("%d\n",  c);//把c的值输出

	return 0;//成功完成
}

#include <stdio.h>

int main()
{
	//定义整型变量a, b, c
	int a;
	int b;
	int c;

	a = 3;
	b = 4;
	c = a + b;
	
	printf("%d\n",  c);//把c的值输出

	return 0;//成功完成
}

#include <stdio.h>

int main()
{
	//extern 关键字只做声明，不能做任何定义，后面还会学习，这里先了解
	//声明一个变量a，a在这里没有建立存储空间
	extern int a;
	a = 10;	//err, 没有空间，就不可以赋值

	int b = 10;	//定义一个变量b，b的类型为int，b赋值为10

	return 0;
}

#include <stdio.h>
#define MAX 10 //声明了一个常量，名字叫MAX，值是10，常量的值一旦初始化不可改

int main()
{
	int a;	//定义了一个变量，其类型为int，名字叫a

	const int b = 10; //定义一个const常量，名为叫b，值为10
	//b = 11; //err,常量的值不能改变

	//MAX = 100;	//err,常量的值不能改变

	a = MAX;//将abc的值设置为MAX的值
	a = 123;

	printf("%d\n", a); //打印变量a的值

	return 0;
}

#include <stdio.h>

int main()
{
	int a = 123;	//定义变量a，以10进制方式赋值为123
	int b = 0567;	//定义变量b，以8进制方式赋值为0567
	int c = 0xabc;	//定义变量c，以16进制方式赋值为0xabc

	printf("a = %d\n", a);
	printf("8进制：b = %o\n", b);
	printf("10进制：b = %d\n", b);
	printf("16进制：c = %x\n", c);
	printf("16进制：c = %X\n", c);
	printf("10进制：c = %d\n", c);
	
	unsigned int d = 0xffffffff; //定义无符号int变量d，以16进制方式赋值
	printf("有符号方式打印：d = %d\n", d);
	printf("无符号方式打印：d = %u\n", d);
	return 0;
}

#include <stdio.h>

int main()
{
	int a;
	printf("请输入a的值：");

	//不要加"\n"
	scanf("%d", &a);
	printf("a = %d\n", a); //打印a的值
    
	return 0;
}

#include <stdio.h>

int main()
{
	short a = 10;
	int b = 10;
	long c = 10l; //或者10L
	long long d = 10ll; //或者10LL

	printf("sizeof(a) = %u\n", sizeof(a));
	printf("sizeof(b) = %u\n", sizeof(b));
	printf("sizeof(c) = %u\n", sizeof(c));
	printf("sizeof(c) = %u\n", sizeof(d));

	printf("short a = %hd\n", a);
	printf("int b = %d\n", b);
	printf("long c = %ld\n", c);
	printf("long long d = %lld\n", d);

	unsigned short a2 = 20u;
	unsigned int b2 = 20u;
	unsigned long c2= 20ul; 
	unsigned long long d2 = 20ull; 

	printf("unsigned short a = %hu\n", a2);
	printf("unsigned int b = %u\n", b2);
	printf("unsigned long c = %lu\n", c2);
	printf("unsigned long long d = %llu\n", d2);

	return 0;
}

#include <stdio.h>

int main()
{
	signed int a = -1089474374; //定义有符号整型变量a
	printf("%X\n", a); //结果为 BF0FF0BA

	//B    F    0    F    F    0    B	 A
	//1011 1111 0000 1111 1111 0000 1011 1010

	return 0;
}

#include <stdio.h>

int main()
{
	unsigned int a = 3236958022; //定义无符号整型变量a
	printf("%X\n", a); //结果为 C0F00F46

	return 0;
}

#include <stdio.h>

int main()
{
	int a;
	int b = sizeof(a);//sizeof得到指定值占用内存的大小，单位：字节
	printf("b = %d\n", b);

	size_t c = sizeof(a);
	printf("c = %u\n", c);//用无符号数的方式输出c的值

	return 0;
}

#include <stdio.h>

int main()
{
	char ch = 'a';
	printf("sizeof(ch) = %u\n", sizeof(ch));

	printf("ch[%%c] = %c\n", ch); //打印字符
	printf("ch[%%d] = %d\n", ch); //打印‘a’ ASCII的值

	char A = 'A';
	char a = 'a';
	printf("a = %d\n", a);		//97
	printf("A = %d\n", A);	//65

	printf("A = %c\n", 'a' - 32); //小写a转大写A
	printf("a = %c\n", 'A' + 32); //大写A转小写a

	ch = ' ';
	printf("空字符：%d\n", ch); //空字符ASCII的值为32
	printf("A = %c\n", 'a' - ' '); //小写a转大写A
	printf("a = %c\n", 'A' + ' '); //大写A转小写a

	return 0;
}

ao@Taoc:~/Desktop/C/2$ ./2.4.1 
sizeof(ch) = 1
ch[%c] = a
ch[%d] = 97
a = 97
A = 65
A = A
a = a
空字符：32
A = A
a = a

#include <stdio.h>

int main()
{
	char ch;
	printf("请输入ch的值：");

	//不要加“\n”
	scanf("%c", &ch);
	printf("ch = %c\n", ch); //打印ch的字符

	return 0;
}

#include <stdio.h>

int main()
{
	printf("abc");
	printf("\refg\n"); //\r切换到句首， \n为换行键

	printf("abc");
	printf("\befg\n");//\b为退格键， \n为换行键

	printf("%d\n", '\123');// '\123'为8进制转义字符，0123对应10进制数为83
	printf("%d\n", '\x23');// '\x23'为16进制转义字符，0x23对应10进制数为35

	return 0;
}

#include <stdio.h>

int main()
{
	//传统方式赋值
	float a = 3.14f; //或3.14F
	double b = 3.14;

	printf("a = %f\n", a);
	printf("b = %lf\n", b);

	//科学法赋值
	a = 3.2e3f; //3.2*1000 = 3200，e可以写E
	printf("a1 = %f\n", a);

	a = 100e-3f; //100*0.001 = 0.1
	printf("a2 = %f\n", a);

	a = 3.1415926f;
	printf("a3 = %f\n", a); //结果为3.141593

	return 0;
}

#include <stdio.h>

int main()
{
	int a = 123;		//十进制方式赋值
	int b = 0123;		//八进制方式赋值， 以数字0开头
	int c = 0xABC;	//十六进制方式赋值

	//如果在printf中输出一个十进制数那么用%d，八进制用%o，十六进制是%x
	printf("十进制：%d\n",a );
	printf("八进制：%o\n", b);	//%o,为字母o,不是数字
	printf("十六进制：%x\n", c);

	return 0;
}

#include <stdio.h>

int main()
{
	int  a = -15;

	printf("%x\n", a);
	//结果为 fffffff1
	//fffffff1对应的二进制：1111 1111 1111 1111 1111 1111 1111 0001
	//符号位不变，其它取反：1000 0000 0000 0000 0000 0000 0000 1110
	//上面加1：1000 0000 0000 0000 0000 0000 0000 1111  最高位1代表负数，就是-15

	return 0;
}

#include <stdio.h>

int main()
{
	char ch;

	//符号位溢出会导致数的正负发生改变
	ch = 0x7f + 2; //127+2
	printf("%d\n", ch);
	//	0111 1111
	//+2后 1000 0001，这是负数补码，其原码为 1111 1111，结果为-127

	//最高位的溢出会导致最高位丢失
	unsigned char ch2;
	ch2 = 0xff+1; //255+1
	printf("%u\n", ch2);
	//	  1111 1111
	//+1后 10000 0000， char只有8位最高位的溢出，结果为0000 0000，十进制为0

	ch2 = 0xff + 2; //255+1
	printf("%u\n", ch2);
	//	  1111 1111
	//+1后 10000 0001， char只有8位最高位的溢出，结果为0000 0001，十进制为1

	return 0;
}

tao@Taoc:~/Desktop/C/2$ gcc 2.7.5.c -o 2.7.5
2.7.5.c: In function ‘main’:
2.7.5.c:15:8: warning: unsigned conversion from ‘int’ to ‘unsigned char’ changes value from ‘256’ to ‘0’ [-Woverflow]
  ch2 = 0xff+1; //255+1
        ^~~~
2.7.5.c:20:8: warning: unsigned conversion from ‘int’ to ‘unsigned char’ changes value from ‘257’ to ‘1’ [-Woverflow]
  ch2 = 0xff + 2; //255+1
        ^~~~
tao@Taoc:~/Desktop/C/2$ ./2.7.5 
-127
0
1

#include <stdio.h>
int main()
{
	int a = 100;
	printf("a = %d\n", a);//格式化输出一个字符串
	printf("%p\n", &a);//输出变量a在内存中的地址编号
	printf("%%d\n");

	char c = 'a';
	putchar(c);//putchar只有一个参数，就是要输出的char
	long a2 = 100;
	printf("%ld, %lx, %lo\n", a2, a2, a2);

	long long a3 = 1000;
	printf("%lld, %llx, %llo\n", a3, a3, a3);

	int abc = 10;
	printf("abc = '%6d'\n", abc);
	printf("abc = '%-6d'\n", abc);
	printf("abc = '%06d'\n", abc);
	printf("abc = '%-06d'\n", abc);

	double d = 12.3;
	printf("d = \' %-10.3lf \'\n", d);

	return 0;
}

#include <stdio.h>

int main()
{
	char ch1;
	char ch2;
	char ch3;
	int a;
	int b;

	printf("请输入ch1的字符：");
	ch1 = getchar();
	printf("ch1 = %c\n", ch1);

	getchar(); //测试此处getchar()的作用

	printf("请输入ch2的字符：");
	ch2 = getchar();
	printf("\'ch2 = %ctest\'\n", ch2);

	getchar(); //测试此处getchar()的作用
	printf("请输入ch3的字符：");
	scanf("%c", &ch3);//这里第二个参数一定是变量的地址，而不是变量名
	printf("ch3 = %c\n", ch3);

	printf("请输入a的值：");
	scanf("%d", &a);
	printf("a = %d\n", a);

	printf("请输入b的值：");
	scanf("%d", &b);
	printf("b = %d\n", b);

	return 0;
}

#include <stdio.h>

int main()
{
	int num = 5;
	printf("s1=%d\n", num / 2);
	printf("s2=%lf\n", num / 2.0);

	return 0;
}

tao@Taoc:~/Desktop/C/3$ ./3.7.1 
S1 = 2
S2 = 2.500000

#include <stdio.h>

int main(){
	float x = 0;
	int i = 0;
	x = 3.6f;
	
	i = x;
	i = (int)x;
	
	printf("x=%f, i=%d\n", x, i);
	
	return 0;
}

#include <stdio.h>

int main()
{
	int a = 1;
	int b = 2;

	if (a > b)
	{
		printf("%d\n", a);
	}

	return 0;
} 

#include <stdio.h>
int main()
{
	int a = 1;
	int b = 2;

	if (a > b)
	{
		printf("%d\n", a);
	}
	else
	{
		printf("%d\n", b);
	}
	return 0;
}

#include <stdio.h>

int main()
{
	unsigned int a;
	scanf("%u", &a);

	if (a < 10)
	{
		printf("个位\n");
	}
	else if (a < 100)
	{
		printf("十位\n");
	}
	else if (a < 1000)
	{
		printf("百位\n");
	}
	else
	{
		printf("很大\n");
	}

	return 0;
}

#include <stdio.h>

int main()
{
	int a = 10;
	int b = 20;
	int c;

	if (a > b)
	{
		c = a;
	}
	else
	{
		c = b;
	}
	printf("c1 = %d\n", c);

	a = 1;
	b = 2;
	c = ( a > b ? a : b );
	printf("c2 = %d\n", c);

	return 0;
}

#include <stdio.h>

int main()
{
	char c;
	c = getchar();

	switch (c) //参数只能是整型变量
	{
	case '1':
		printf("OK\n");
		break;//switch遇到break就中断了
	case '2':
		printf("not OK\n");
		break;
	default://如果上面的条件都不满足，那么执行default
		printf("are u ok?\n");
	}
	return 0;
}

#include <stdio.h>

int main()
{
	int a = 20;
	while (a > 10)
	{
		scanf("%d", &a);
		printf("a = %d\n", a);
	}

	return 0;
}

#include <stdio.h>

int main()
{
	int a = 1;
	do
	{
		a++;
		printf("a = %d\n", a);
	} while (a < 10);

	return 0;
}

#include <stdio.h>

int main()
{
	int i;
	int sum = 0;
	for (i = 0; i <= 100; i++)
	{
		sum += i;

	}

	printf("sum = %d\n", sum);

	return 0;
}

#include <stdio.h>

int main()
{
	int num = 0;
	int i, j, k;
	for (i = 0; i < 10; i++)
	{
		for (j = 0; j < 10; j++)
		{
			for (k = 0; k < 10; k++)
			{
				printf("hello world\n");
				num++;
			}
		}
	}

	printf("num = %d\n", num);

	return 0;
}

#include<stdio.h>

int main()
{
	int sum = 0;           //定义变量sum

	for (int i = 1; i <= 100; i++)
	{
		if (i % 2 == 0)   //如果i是一个偶数，执行if语句中的代码
		{
			continue;      //结束本次循环
		}
		sum += i;          //实现sum和i的累加
	}

	printf("sum = %d\n", sum);

	return 0;
}

#include <stdio.h>

int main()
{
	goto End; //无条件跳转到End的标识
	printf("aaaaaaaaa\n");

End:
	printf("bbbbbbbb\n");

	return 0;
}

tao@Taoc:~/Desktop/C/4$ ./4.4.3 
bbbbbbbb

int a[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };//定义一个数组，同时初始化所有成员变量
int a[10] = { 1, 2, 3 };//初始化前三个成员，后面所有元素都设置为0
int a[10] = { 0 };//所有的成员都设置为0
//[]中不定义元素个数，定义时必须初始化
int a[] = { 1, 2, 3, 4, 5 };//定义了一个数组，有5个成员

#include <stdio.h>

int main()
{
	int a[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };//定义一个数组，同时初始化所有成员变量

	printf("a = %p\n", a);
	printf("&a[0] = %p\n", &a[0]);

	int n = sizeof(a); //数组占用内存的大小，10个int类型，10 * 4  = 40
	int n0 = sizeof(a[0]);//数组第0个元素占用内存大小，第0个元素为int，4

	int i = 0;
	for (i = 0; i < sizeof(a) / sizeof(a[0]); i++)
	{
		printf("%d ", a[i]);
	}
	printf("\n");

	return 0;
}

#include <stdio.h>

int main()
{
	// 定义一个二维数组，名字叫a
    // 由3个一维数组组成，这个一维数组是int[4]
    // 这3个一维数组的数组名分别为a[0],a[1],a[2]
    int a[3][4];
    
    a[0][0] = 0;
    
    a[2][3] = 12;
    
    // 给数组每个元素赋值
    int i = 0;
    int j = 0;
    int num = 0;
    
    for(i=0; j < 4; i++)
    {
        for(j = 0; j < 4; j++)
        {
            a[i][j] = num++;
        }
    }
    
    // 遍历数组，并输出每个成员的值
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 4; j++)
        {
            printf("%d", a[i][j]);
        }
        printf("\n");
    }
    
    return 0;
    
}

//分段赋值 	int a[3][4] = {{ 1, 2, 3, 4 },{ 5, 6, 7, 8, },{ 9, 10, 11, 12 }};

int a[3][4] = 
	{ 
		{ 1, 2, 3, 4 },
		{ 5, 6, 7, 8, },
		{ 9, 10, 11, 12 }
	};
	// 连续赋值
	int a[3][4] = { 1, 2, 3, 4 , 5, 6, 7, 8, 9, 10, 11, 12  };
	// 可以只给部分元素赋初值，未初始化则为0
	int a[3][4] = { 1, 2, 3, 4  };
	
	//所有的成员都设置为0
	int a[3][4] = {0};
	
	//[]中不定义元素个数，定义时必须初始化
	int a[][4] = { 1, 2, 3, 4, 5, 6, 7, 8};

#include <stdio.h>

int main()
{
	//定义了一个二维数组，名字叫a
	//二维数组是本质上还是一维数组，此一维数组有3个元素
//每个元素又是一个一维数组int[4]
	int a[3][4] = { 1, 2, 3, 4 , 5, 6, 7, 8, 9, 10, 11, 12  };

	//数组名为数组首元素地址，二维数组的第0个元素为一维数组
	//第0个一维数组的数组名为a[0]
	printf("a = %p\n", a);
	printf("a[0] = %p\n", a[0]);
	
	//测二维数组所占内存空间，有3个一维数组，每个一维数组的空间为4*4
	//sizeof(a) = 3 * 4 * 4 = 48
	printf("sizeof(a) = %d\n", sizeof(a));

	//测第0个元素所占内存空间，a[0]为第0个一维数组int[4]的数组名，4*4=16
	printf("sizeof(a[0]) = %d\n", sizeof(a[0]) );

	//测第0行0列元素所占内存空间，第0行0列元素为一个int类型，4字节
	printf("sizeof(a[0][0]) = %d\n", sizeof(a[0][0]));

	//求二维数组行数
	printf("i = %d\n", sizeof(a) / sizeof(a[0]));

	// 求二维数组列数
	printf("j = %d\n", sizeof(a[0]) / sizeof(a[0][0]));

	//求二维数组行*列总数
	printf("n = %d\n", sizeof(a) / sizeof(a[0][0]));

	return 0;
}

tao@Taoc:~/Desktop/C/5$ ./5.3.3 
a = 0x7ffe09fd1e60
a[0] = 0x7ffe09fd1e60
sizeof(a) = 48
sizeof(a[0]) = 16
sizeof(a[0][0]) = 4
i = 3
j = 4
n = 12

int a[3][4][5];

#include <stdio.h>

int main(){
	// int a[3][4][5]; //定义了一个三维数组，有3个二维数组int[4][5]
	int a[3][4][5] = { { { 1, 2, 3, 4, 5 }, { 6, 7, 8, 9, 10 }, { 0 }, { 0 } }, { { 0 }, { 0 }, { 0 }, { 0 } }, { { 0 }, { 0 }, { 0 }, { 0 } } };
    int i, j, k;
	for (i = 0; i < 3; i++)
	{
		for (j = 0; j < 4; j++)
		{
			for (k = 0; k < 5; k++)
			{
				//添加访问元素代码
				printf("%d, ", a[i][j][k]);
			}
			printf("\n");
		}
	}
	return 0;
}

tao@Taoc:~/Desktop/C/5$ ./5.4 
1, 2, 3, 4, 5, 
6, 7, 8, 9, 10, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 
0, 0, 0, 0, 0,