第四章

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

    return 0;
}

4-3

#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;
}

4-4

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

    printf("Enter a number:");
    scanf("%d",&m);
    for(i=2;i<=m/2;i++)
        if(m%i==0)
            break;
    if(i>m/2&&m!=1)
        printf("%d is a prime number!\n",m);
    else
        printf("No!\n");

    return 0;
}

4-5

#include<stdio.h>
int main(void)
{
    int mynumber=38;
    int count=0,yournumber;
    for(count=1;count<=5;count++){
        printf("Input your number:");
        scanf("%d",&yournumber);
        if(yournumber==mynumber){
            printf("Ok!you are right!\n");
            break;
        }
        else
            if(yournumber>mynumber)
                printf("Sorry!your number is bigger than my number!\n");
            else
                printf("Sorry!your number is smaller than my number!\n");
    }
    printf("Game is over!\n");

    return 0;
}

4-6

#include<stdio.h>
double fact(int n);
int main(void)
{
    int i;
    double sum;
    sum=0;
    for(i=1;i<=100;i++)
        sum=sum+fact(i);
    printf("1!+2!+...+100!=%e\n",sum);

return 0;
}
double fact(int n)
{
    int i;
    double result;

    result=1;
    for(i=1;i<=n;i++)
        result=result*i;

    return result;
}

4-7

#include<stdio.h>
int main(void)
{
  int i,j;
  double item,sum;

  sum=0;
  for(i=1;i<=100;i++){
      item=1;
      for(j=1;j<=i;j++)
          item=item*j;
      sum=sum+item;
  }
  printf("1!+2!+...+100!=%e\n",sum);

  return 0;
}

4-8

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

    printf("Enter n:");
    scanf("%d",&n);
    printf("Enter %d marks:",n);
    scanf("%d",&mark);
    max=mark;
    for(i=1;i<n;i++){
        scanf("%d",&mark);
        if(max<mark)
            max=mark;
    }
    printf("Max=%d\n",max);

    return 0;
}

4-9

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

    printf("Enter x:");
    scanf("%d",&x);
    while(x!=0){
        printf("%d",x%10);
        x=x/10;
    }

    return 0;
}

4-10

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

    count=0;
    for(m=2;m<=100;m++){
        n=sqrt(m);
        for(i=2;i<=n;i++)
            if(m%i==0)
                break;
            if(i>n){
            printf("%6d",m);
            count++;

            if(count%10==0)
                printf("\n");
            }
    }
    printf("\n");

    return 0;
}

4-11

#include<stdio.h>
int main(void)
{
    int i,x1,x2,x;

    x1=1;
    x2=1;
    printf("%6d%6d",x1,x2);
    for(i=1;i<=8;i++){
        x=x1+x2;
        printf("%6d",x);
        x1=x2;
        x2=x;
    }
    printf("\n");

    return 0;
}

4-12

#include<stdio.h>
int main(void)
{
    int child,men,women;

    for(men=0;men<=45;men++)
        for(women=0;women<=45;women++)
            for(child=0;child<=45;child++)
                if(men+women+child==45&&men*3+women*2+child*0.5==45)
                    printf("men=%d,women=%d,child=%d\n",men,women,child);

    return 0;
}