作业3

1.

#include<stdio.h>
int main(void)
{
    int x,y;
    printf("Enter x:\n");
    scanf("%d",&x);
    if(x<0){
      y = -1;
    }
    else if(x==0){
      y=0;
    }
    else{


        y=1;
        
    }
   printf("y=%d\n",y); 
   return 0;
}

2.

#include<stdio.h>
int main (void)
{
    int count,i,n;
    double grade,total;

    printf("Enter n:");
    scanf("%d",&n);
    total=0;
    count=0;
    for(i=1;i<=n;i++){
        printf("Enter grade#%d:",i);
        scanf("%Lf",&grade);
        total=total+grade;
        if(grade>=60){
            count++;
        }
    }
    printf("Grade average=%.2f\n",total/n);
    printf("Number of failures=%d\n",count);
    
    return 0;
}

3.

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



        blank++;
    else
        other++;
    }

printf("blank=%d,digit=%d,letter=%d,other=%d\n",blank,digit,letter,other);
    return 0;
}

4.

#include<stdio.h>
int main(void)
{
    int i,n,year;
    printf("Enter n:");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        printf("Enter year\n:");
        scanf("%d",&year);
        if((year%4==0&&year%100!=0)||(year%400==0)){
            printf("没有错，这是闰年~\n");
        }
        else{
            printf("很可惜，这不是闰年~\n");
        }
    }


        return 0;

    }

5.

#include<stdio.h>
int main(void)
{
    char op;
    printf("输入成绩等级:");
    scanf("%c",&op);
    switch(op){
        case'A':printf("grade=90-100");
            break;
        case'B':printf("grade=80-89");
            break;
        case'C':printf("grade=70-79");
            break;
        case'D':printf("grade=60-69");
            break;
        case'E':printf("grade=0-59");
            break;
    }
    return 0;
}

6.

#include<stdio.h>
int main(void)
{
    int choice,i;
    double price;
    for(i=1;i<=5;i++){
        printf("[1]select apples\n");
        printf("[2]select pears\n");
        printf("[3]select oranges\n");
        printf("[4]select grapes\n");
        printf("[0]select Exit\n");
        printf("Enter choice:");
        scanf("%d",&choice);
        if(choice==0)
            break;
        switch(choice){
               case 1:price= 3.00;break;
               case 2:price=2.50;break; 
               case 3:price=4.10;break; 
               case 4:price=10.20;break;
            default:price=0.00;break;
            }
            printf("price=%0.2f\n",price);
        }
        printf("Thanks\n");
        return 0;
    }