20131003国庆作业第四章例4-1,4-2,4-3.

#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\n",pi);

return 0;
}

#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\n",total/num);
printf("Number of failures is %d\n",count);
}
else
printf("Grade average is 0\n");

return 0;
}

#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.\n",count);

return 0;
}