作业3

1.

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

    printf("Enter x:");
    scanf("%d",&x);

    if (x<0){
        printf("y=sign(%d)=-1
",x);
    }
    else if (x=0){
        printf("y=sign(%d)=0
",x);
    }
    else {
        printf("y=sign(%d)=1
",x);
    }

    return 0;
}

2.

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

    total = 0;
    count = 0;

    printf("Enter n:");
    scanf("%d",&n);

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

3.

#include<stdio.h>
int main(void)
{
    int digit,letter,other;
    char ch;
    int i;
    digit = 0;
    letter = 0;
    other = 0;
    printf("Enter characters:");
    for (i=1;i<=15;i++){
        ch = getchar( );
        if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
            letter = letter + 1;
        else if(ch>='0'&&ch<='9')
            digit = digit + 1;
        else
            other = other + 1;
    }
    printf("letter=%d,digit=%d,other=%d",letter,digit,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:");
    scanf("%d",&year);

        if (year == -1){
        break;
    }
    else if ((year%4 == 0 && year%100!=0)||(year%400 == 0)){
        printf("该年为闰年。
");
    }
    else {
        printf("该年不为闰年。
");
    }
    }

    return 0;
}

5.

#include<stdio.h>
int main(void)
{
    char op;

    printf("Type in the word:");
    scanf("%c",&op);
    switch(op){
    case'A':
        printf("90-100
");
        break;
    case'B':
        printf("80-89
");
        break;
    case'C':
        printf("70-79
");
        break;
    case'D':
        printf("60-69
");
        break;
    case'E':
        printf("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]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=3.00;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=%.2f
",price);
    }

    return 0;
}