#include<stdio.h>
double sign(int x)
{
    double y;
    if(x>0) y=1;
    else if(x<0) y=-1;
    else y=0;
    return y; 
}
int main()
{
    int x;
    double y;
    printf("Input x:");
    scanf("%d",&x);
    y=sign(x);
    printf("f(x)=%.0lf",y);
    return 0;
}

#include<stdio.h>
double even(int n)
{
    if(n%2==0) return 1;
    else return 0;
}
int main()
{
    int n,sum=0;
    double num;
    printf("Input n:\n");    
    while(n>0){
        scanf("%d",&n);
        num=even(n);
        if(0==num){
            printf("是奇数\n");
        sum=sum+n;
        }
        else if(1==num){
            printf("是偶数\n");
        }
        else{
            printf("Unknow");
        }
    }
    printf("奇数和=%d",sum);
    return 0;    
}

#include<stdio.h>
#include<math.h>
int prime(int m){
    int i,n;
    if(m==1)return 0;
    n=sqrt(m);
    for(i=2;i<=n;i++)
    if(m%i==0){
        return 0;
    }
    return 1;
}
int main()
{
    int sum=0,m,h=0,n;/*h为素数合*/ 
    printf("Input m,n:");
    scanf("%d%d",&m,&n);/*1<=m n<=500*/
    for(m;m<=n;m++){
        if(prime (m)!=0){
            h=h+m;
            sum++;
        }
    }
    printf("素数的个数为:%d,素数的合为:%d",sum,h);
    return 0;
}

#include<Stdio.h>                                   
#include<math.h>                                                              
double countdigit(int number,int digit)           
{                                                   
    int n,digit1,i,y=0;                           
    double sum,sum1=0;                                          
    digit1=number*10;
    scanf("%d",&n);                                  
    for(i=1;i<=n;i++){                   
        digit1=digit1/10;
        y=digit1%10;
        if(y==digit){
        sum1++;        
        }
    }
    printf("该数字中%d的个数为%.0lf",digit,sum1);
    return sum;                                    
}
int main()                                          
{                                                   
    int digit=0,y=0,number,i,n;                           
    double sum,sum1=0;                                                                                        
    printf("Input number,digit,n(n为输入数字位数):");
    scanf("%d%d",&number,&digit);
    sum=countdigit(number,digit);               
    return 0;                                                
}

#include<stdio.h>
#include<math.h>
int number(int m,int n){    
        for(m;m<n;m++){
        int digit=m;
        int digit1=0,digit2=0,digit3=0;        
        digit1=digit/100;digit%=100;
        digit2=digit/10;        
        digit3=digit%10;
        if(pow(digit1,3)+pow(digit2,3)+pow(digit3,3)==m){
        printf("%dê????é?¨êy\n",m); 
        }            
    }return 0;
}
int main()
{
    int m,n;
    printf("Input m,n:");
    scanf("%d%d",&m,&n);
    number(m,n);
    return 0;
}