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基本输入输出
void main()
{
	int a,b,sum;
	printf("Please input information:\n");
	scanf("%d%d",&a,&b);
	sum=a+b;
	printf("Sum is %d\n",sum);
}
不同格式输出(o表示8进制,x表示16进制)
void main()
{
	int a=8;int b=15;
	printf("%o,%x,%s\n",a,b, "china");
}
基符号常量(简单文本替换)
#define PI 3.1415
void main()
{
	double radius,area;
	cin>>radius;
	area=radius*radius*PI;
	printf("Area is %f",area);
}
数学函数
#include<math.h>
void main()
{
	float x,y;
	printf("输入 x :");
	scanf("%f",&x);
	if (x!=0) y=sin(x)/x;
	else y=1;
	printf("x=%5.2f\ty=%5.2f\n",x,y);
}
强制类型转换
void main()
{
	float f=5.63;
	int i=(int)f;
	printf("(int)f=%d",i);
}
单个字符的输入和输出
void main()
{
	char c;
	c=getchar();
	putchar(c);
	putchar('a'-32);
}
格式化输出
void main()
{
	int a=121;
	printf("%5d",a);
	printf("%-8d",a);
	printf("%08d",a);

	int b=15;
	printf("%d,%o,%x",b,b,b);

	double c=123.456;
	printf("%f",c);
	printf("%5.3f",c);
	printf("%-7.2f",c);

	printf("%-4c",'A');
	printf("%20s","Hello");
}
实数的输入输出
void main()
{
	float fx,fy;
	scanf("%f%e",&fx,&fy);
	printf("%f %f",fx,fy);
	double dx;
	scanf("%lf",&dx);
	printf("%.4lf",dx);
}
字符串的输入输出
void main()
{
	char str1[10],str2[10];
	scanf("%s",str1);
	scanf("%10s",str2);
	printf("%-10s,%10s",str1,str2);
}
if与switch语句
void main()
{
	int a=2,b=3;
	if(a>b)
		printf("a>b");
	else
		printf("b>a");

	int day;
	scanf("%d",&day);
	switch(day)
	{
	case 1:
		printf("Monday");
		break;
	case 2:
		printf("Tuesday");
		break;
	case 3:
		printf("Wednesday");
		break;
	default:
		printf("Fuck");
	}
}
while语句
void main()
{
	int i=0,sum=0;
	while(i<=10)
	{
		sum+=i;
		i++;
	}
	printf("%d",sum);
}
do,while语句
void main()
{
	int i=0,sum=0;
	do
	{
		sum+=i;
		i++;
	}while(i<=10);
	printf("%d",sum);
}
for循环
void main()
{
	int i=0,sum=0;
	for(;i<=10;i++)
	{	sum+=i;	}
	printf("%d",sum);
}
break与continue语句
void main()
{
	int i=0,sum=0;
	for(;i<=100;i++)
	{
		if(0==i%2)
			continue;
		if(81==i)
			break;
		sum+=i;
	}
	printf("%d",sum);
}
一维数组
void main()
{
	int a[5]={1,2,3,4,5};
	int b[]={6,7,8,9,10};
	int c[5]={11,12,13};
	for(int i=0;i<5;i++)
		printf("%d,%d,%d\n",a[i],b[i],c[i]);
	for(i=3;i<5;i++)
		scanf("%d",&c[i]);
	printf("%d,%d",c[3],c[4]);
}
二维数组
void main()
{
	int a[2][3]={{1,2,3},{4,5,6}};
	int b[2][3]={1,2,3,4,5,6};
	int c[2][3]={1,2,3,4};
	for(int i=0;i<2;i++)
		for(int j=0;j<3;j++)
			printf("%d,%d,%d\n",a[i][j],b[i][j],c[i][j]);
}
字符数组
void main()
{
	char a[5]={'h','e','l','l','o'};
	char b[6]="hello";
	char c[]="hello";
	puts(b);
	puts(c);
	gets(a);
	puts(a);
	scanf("%s",a);
	printf("%s",a);
}
字符串函数
#include"string.h"
void main()
{
	char a[20]="Hello";
	char b[20]="World";
	strcat(a,b);
	puts(a);
	strcpy(a,b);
	puts(a);
	printf("%d\n",strlen(b));
	if(0==strcmp(a,b))
		printf("Same");
	else if(strcmp(a,b)>0)
		printf("a is bigger");
	else
		printf("b is bigger");
}
基本函数调用
void main()
{
	int Max(int a,int b);
	int a,b;
	scanf("%d%d",&a,&b);
	printf("Bigger one is %d\n",Max(a,b));
}
int Max(int a,int b)
{	return a>b?a:b;	}
引用

声明时必须初始化

void main()
{
	int a=1;
	int &b=a;   
	printf("%d\n",b);
	b=2;
	printf("%d\n",a);
}
引用做参数
void Swap(int &a,int &b)
{
	int temp=a;
	a=b;
	b=temp;
}
void main()
{
	int a=1,b=2;
	printf("%a=%d,b=%d\n",a,b);
	Swap(a,b);
	printf("%a=%d,b=%d\n",a,b);
}
宏定义

简单的文本替换，没有类型，不做任何类型检查

#define PI 3.1515926
#define Max(X,Y)   ((X)>(Y)?(X):(Y))
void main()
{
	double radius=3,area;
	area=PI*radius*radius;
	printf("%lf\n",area);
	float a=3.14,b=3.15,c;
	c=Max(a,b);
	printf("%.2f\n",c);
}
条件编译
#define DEBUG
void main()
{
	#ifdef DEBUG
		printf("DEBUG is defined!\n");
	#else
		printf("DEBUG is not defined!\n");
	#endif
}
/////////////////////
void main()
{
	#ifndef DEBUG
		printf("DEBUG is not defined!\n");
	#else
		printf("DEBUG is defined!\n");
	#endif
}
指针
void main()
{
	int a=4,b=5;
	int *p1=&a,*p2;
	p2=&b;
	printf("%d,%d\n",*p1,*p2);

	scanf("%d",p1);
	printf("%d\n",*p1);

	p1=p2;
	printf("%d\n",*p1);

	int c[5]={1,2,3,4,5};
	p2=c;  //p2=&c[0];
	for(int i=0;i<5;i++)
		printf("%d\n",*(p2+i));		//printf("%d\n",*(p2++));

	char *ps;
	ps="Hello";   //char *ps="Hello";
	puts(ps);
}
/////////////////////
void Swap(int *p1,int *p2)
{
	int temp=*p1;
	*p1=*p2;
	*p2=temp;
}
void main()
{
	int a=1,b=2;
	int *p1=&a,*p2=&b;
	printf("a=%d,b=%d\n",a,b);
	//Swap(&a,&b);
	Swap(p1,p2);
	printf("After Swap,a=%d,b=%d\n",a,b);
}
/////////////////////
void main()
{
	int a[3][3]={1,8,9,6,5,4,7,3,2},max;
	int (*p)[3];  //指向数组的指针
	p=a;
	max=**p;
	for(int i=0;i<3;i++)
		for(int j=0;j<3;j++)
			if(max<*(*p+j))
				max=*(*p+j);
			printf("The biggest one is %d\n",max);
}
函数指针(指向函数的指针)
int Max(int a,int b)
{	return a>b?a:b;	}
void main()
{
	int a=3,b=4,c;
	int (*fun)(int ,int);
	fun=Max;
	c=(*fun)(a,b);
	printf("The bigger one is %d\n",c);
}
指针型函数(返回值是指针)
char *GetDay(int number)
{
	char*day[8]={"Illegalday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};  //指针数组
	return (number<7||number>1)?day[number]:day[0];
}
void main()
{
	int day;
	printf("请输入数字:\n");
	scanf("%d",&day);
	puts(GetDay(day));
}
指向指针的指针
void main()
{
	char *name[]={"John","Sophia","Mark","Marry"};
	char **p;
	for(int i=0;i<4;i++)
	{
		p=name+i;
		printf("%s\n",*p);
	}
}
结构体
void main()
{
	struct student{
		long int number;  //不能在结构体内初始化
		char name[20];
		float score;
	};
	struct student stu={20110316,"John",98.9};
	printf("Name:%s , Number:%d , Score:%.1f \n",stu.name,stu.number,stu.score);
	struct student *stup=&stu;
	printf("Name:%s , Number:%d , Score:%.1f \n",stup->name,stup->number,stup->score);
}
动态内存分配
#include "stdlib.h"
#include "string.h"
struct student
{
	char name[20];
};
void main()
{
	struct student *p;
	p=(struct student*)malloc(sizeof(struct student));
	if(p==NULL)
	{
		printf("Out of Memory!\n");
		exit(-1);
	}
	strcpy(p->name,"John");
	printf("%s\n",p->name);
	free(p);
}
联合
union myInfo
{
	int age;
	double score;
};
void main()
{
	union myInfo m,n;
	m.age=10;
	n.score=99.9;
	printf("%d,%lf\n",m.age,n.score);
}