20131003国庆作业第四章例4-1,4-2,4-3.

4-1

#include<stdio.h>
#include<math.h>
int main(void)
{
    int denominator,flag;
    double item,pi;

    flag=1;
    denominator=1;
    item=1.0;
    pi=0;

    while(fabs(item)>=0.0001){
        item=flag*1.0/denominator;
        pi=pi+item;
        flag=-flag;
        denominator=denominator+2;
    }
    pi=pi*4;
    printf("pi=%.4f
",pi);

    return 0;
}

4-2

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

    num=0;
    total=0;
    count=0;
    printf("Enter grades:");
    scanf("%lf",&grade);

    while(grade>=0){
        total=total+grade;
        num++;
        if(grade<60)
            count++;
        scanf("%lf",&grade);
    }
    if(num!=0){
        printf("Grade average is %.2f
",total/num);
        printf("Number of failures is %d
",count);
    }
    else
        printf("Grade average is 0
");

    return 0;
}

4-3

运行结果1

结果2

#include<stdio.h>
int main(void)
{
    int count,number;

    count=0;
    printf("Enter a number:");
    scanf("%d",&number);
    if(number<0)number=-number;
    do{
        number=number/10;
        count++;
    }while(number!=0);
    printf("It contains %d digits.
",count);

    return 0;
}