1，有几位数字

#include<stdio.h>


int main_2_1_digit(){
	int n;

	while(scanf("%d",&n)){
		int count = 0;
		if(n==0)
			count = 1;
		while(n){
			count++;
			n/=10;
		}
		
		printf("%d\n",count);
	}
	return 0;
}

2，三位数的三个数字

#include<stdio.h>


int main_2_2_daffodil(){

	int i,j,k;

	for(int n=100;n<=999;n++){
		i = n % 10;
		j = (n/10) % 10;
		k = (n/100) % 10;

		if( n == i*i*i + j*j*j + k*k*k){
			printf("%d\n",n);
		}
	}


	return 0;
}

3，韩信点兵

#include<stdio.h>

int main_2_3_hanxin(){

	int a,b,c;
	int i,sum;

	while(scanf("%d%d%d",&a,&b,&c)){
		sum = -1;
		for(i=10;i<=100;i++){
			if(i%3 == a && i%5 == b && i%7 == c){
				sum =i;
				break;
			}
		}
		
		if(sum == -1){
			printf("No answer\n");
		}else{
			printf("%d\n",sum);
		}
	}

	
	return 0;
}

4，打印倒三角

#include<stdio.h>

int main_2_4_triangle(){

	int n;
	int i,j;

	while(scanf("%d",&n)){
		
		for(i=n;i>0;i--){
			for(j=1;j < n;j++){
				if(j+i >= n+1){
					printf("#");
				}else{
					printf(" ");
				}
			}

			printf("#");

			for(j=n+1;j < 2*n;j++){
				if(j-i <= n-1){
					printf("#");
				}else{
					printf(" ");
				}
			}
			
			printf("\n");
		}
	
	}

	
	return 0;
}

5，输入n个数，比m小的

#include<stdio.h>

int main_2_5_stat(){
	int arr[1000];
	int n,m;
	int i;
	int count;

	while(scanf("%d",&n)){
		for(i=0;i<n;i++){
			scanf("%d",&arr[i]);
		}
		scanf("%d",&m);
		
		count=0;
		for(i=0;i<n;i++){
			if(m > arr[i]){
				count++;
			}
		}

		printf("%d\n",count);
	}

	
	return 0;
}

6，数aabb

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

int main_aabb_complete(){

	int a,b,n;
	double m;

	for(a=1;a<=9;a++){
		for(b=0;b<=9;b++){
			n=a*1100 + b*11;
		
			m=sqrt((double)n);

			//判断m是否为整数
			//进行浮点数比较的时候要考虑浮点误差
			if(floor(m+0.5) == m){
				printf("%d     %lf\n",n,m);
			}
		}
	}
	

	getchar();
	return 0;
}

7，浮点数陷阱

#include<stdio.h>


int main_float_trap(){

	double i;

	for(i=9;i!=10;i+=0.1){
	
		printf("%.1lf\n",i);
	
		if(i>10){
			break;
		}
	}

	
	return 0;
}

8，varble_no_init

#include<stdio.h>

int main_varble_no_init(){

	int a,b,c;

	printf("%d %d %d",a,b,c);

	scanf("%d",&a);

	return 0;

}

9，全排列

#include<stdio.h>


int n = 0;
void swap(int *a,int *b){
	int m = *a;
	*a = *b;
	*b = m;
}

void perm(int list[],int k,int m){
	int i;

	if(k > m){
		for(i=0;i<=m;i++){
			printf("%d ",list[i]);
		}
		printf("\n");
		n++;
	}else{
		for(i=k;i<=m;i++){
			swap(&list[k],&list[i]);
			perm(list,k+1,m);
			swap(&list[k],&list[i]);
		}
	}
}

int main_quan_pai_lie_version_1(){
	int list[] = {1,2,3,4,5};

	perm(list,0,4);

	printf("total: %d\n",n);

	return 0;
}