作业三

#include<stdio.h>
int main(void)
{
    int x,y;

    printf("Enter x:");
    scanf("%d",&x);
    if(x>0){
        y=1;
    } 
    else if(x==0){ y=0;
    } 
    else if(x<0) { y=-1;
    }
    printf("y=%d",y); 
    return 0;
}

#include<stdio.h>
int main(void)
{
    int count,i,n;  
    double grade,sum;
    
    printf("Enter n:");
    scanf("%d",&n);
    sum=0;
    count=0;

    for(i=1;i<=n;i++){
    printf("Enter grade#%d:",i);
    scanf("%Lf",&grade);
    sum=sum+grade;
    if(grade>=60)
      count++;
    }
printf("平均成绩=%.3f
",sum/n);
printf("及格人数=%d
",count);
return 0;
}

#include<stdio.h>
int main(void)
{
    int letter,blank,digit,other;
    char ch;
    int i;
    letter=blank=digit=other=0;

    printf("Enter 15 characters:");
    for(i=1;i<=15;i++){
        ch=getchar();
        if((ch>='a'&& ch<='z')||(ch>='A'&& ch<='Z'))
        letter++;
        else if(ch>='0'&&ch<='9')
        digit ++;
        else if((ch>=' '&&ch<=' ')||(ch>='
'&&ch<='
'))
        blank++;
        else
        other++;
    }
    printf("letter=%d,digit=%d,blank=%d,other=%d
",letter,digit,blank,other);
    return 0;
}

#include<stdio.h>
int main(void)
{
    int year,n,i;

    printf("Enter n:");
    scanf("%d",&n);
    
    for(i=1;i<=n;i++){
        printf("Enter year:");
        scanf("%d",&year);
    if(year==-1)
        break;
  if((year%4==0&&year%100!=0)||(year%400==0)){
    printf("这一年是闰年
");
    }
    else
    printf("这一年不是闰年
");    
        
    }
return 0;    
}

#include<stdio.h>
int main()
{
    char ch;
    printf("输入成绩等级:");
    ch=getchar();
    switch(ch){
        case 'A':
        printf("A对应90-100
");
        break;
        case 'B':
        printf("B对应80-89
");
        break;
        case 'C':
        printf("C对应70-79
");
        break;
        case 'D':
        printf("D对应60-69
");
        break;
        case 'E':
        printf("E对应0-59
");
        break;
        default:
        printf("结束
");
        break;
        
    }
    return 0;
    
}

#include<stdio.h>
int main(void)
{
    int choice,i;
    double price;
    for(i=1;i<=5;i++){
        printf("[1]apples
");
        printf("[2]pears
");
        printf("[3]oranges
");
        printf("[4]grapes
");
        printf("[0]exit
");
        
        printf("Enter choice:");
        scanf("%d",&choice);
        if(choice==0)
        break;
        switch(choice){
            case 1:price=3.0;break;
            case 2:price=2.5;break;
            case 3:price=4.10;break;
            case 4:price=10.20;break;
            default:price=0.0;break;
        }
        printf("price=%.2f
",price);
        }
       printf("Thanks
");
      return 0;
}