#include <stdio.h>
#include <math.h>

int main(){
	double x,y;
	scanf("%lf",&x);
	if(x<0){
		y=pow(x,5)+2*x+1.0/x;
	}
	else{
		y=sqrt(x);
	}
	
	printf(".2lf",y);
	return 0;
}

for循环

前n项和

#include <stdio.h>

int main(){
	int n;
	double sum=0;
	scanf("%d",&n);
	int flag=1;//标记正负号 
	for(int i=1;flag<=n;i+=2){
		if(flag%2!=0){//flag为奇数 
			sum+=1.0/i;
		}
		else {
			sum-=1.0/i;//flag为偶数 
		}
		flag++;
	}
	
	printf("%lf",sum);
	return 0;
}

n的阶乘

乘方表与阶乘表

#include <stdio.h>
#include <math.h>
int main(){
	int n;
	scanf("%d",&n);
	for(int i=0;i<=n;i++){
		printf("2^%d = %.lf\n",i,pow(2,i));
	}
	
	return 0;
}

?pow的返回为double类型，若使用以下语句则输出都为0

printf("2^%d = %d\n",i,pow(2,i));

#include <stdio.h>
#include <math.h>

double fact(int n){
	double ans=1;
	for(int i=1;i<=n;i++){
		ans*=i;
	} 
	return ans;
}

int main(){
	int n;
	scanf("%d",&n);
	for(int i=0;i<=n;i++){
		printf("%d! = %.lf\n",i,fact(i));
	}
	
	return 0;
}

分支结构

if-else

#include <stdio.h>

int main(){
	int letter=0,digit=0,other=0;
	char a;
	for(int i=0;i<10;i++){
		a=getchar();
		if((a>='a'&&a<='z')||(a>='A'&&a<='Z')) letter++;
		else if(a>='0'&&a<='9') digit++;
		else other++;
	}	
	
	printf("letter=%d\n",letter);
	printf("digit=%d\n",digit);
	printf("other=%d\n",other);
	return 0;
}

?switch

#include <stdio.h>

int main(){
	double a,b;
	char c;
	scanf("%lf%c%lf",&a,&c,&b);
	switch(c){
		case '+':
			printf("%lf + %lf = %lf\n",a,b,a+b);
			break;
		case '-':
			printf("%lf - %lf = %lf\n",a,b,a-b);
			break;
		case '*':
			printf("%lf * %lf = %lf\n",a,b,a*b);
			break;
		case '/':
			if(b==0) printf("error\n");
			else printf("%lf / %lf = %lf\n",a,b,a/b);
			break;
	}
	
	return 0;
}

?循环结构

while

#include <stdio.h>

int main(){
	double sum=0;//分数之和，定义为double类型 
	int i=1,j=1;//i为分母 ,j用来区分奇数项还是偶数项 
	while(1.0/i>1e-6){//题目要求精确到小数点后4位，比题目要求更精确方便四舍五入 
		if(j%2!=0){//奇数项 
			sum+=1.0/i;
		}
		else{
			sum-=1.0/i;
		} 
		i+=2;//i每次加2 
		j++;
	}
	
	double ans=sum*4;
	printf("%.4lf",ans);//控制输出小数点后4位 
	return 0;
}