第四章例题、心得及问题。

例题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;
}

例题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);}elseprintf("Grade average is 0\n");return 0;
}

例题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;
}

运行结果1：

运行结果2：

例题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);elseprintf("No!\n");return 0;
}

运行结果1：

运行结果2：

例题4-5：

#include<stdio.h>
int main(void)
{int mynumber=44;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;}elseif(yournumber>mynumber)printf("Sorry!your number is bigger than my number!\n");elseprintf("Sorry!your number is smaller than my number!\n");}printf("Game is over!\n");return 0;
}

例题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;
}

例题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;
}

例题4-8-1：

#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;
}

例题4-8-2：

#include<stdio.h>
int main(void)
{int mark,max;printf("Enter marks:");scanf("%d",&mark);max=mark;while(mark>=0){if(max<mark)max=mark;scanf("%d",&mark);};printf("Max = %d\n",max);return 0;
}

例题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;
}

例题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;
}

例题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;
}

例题4-12-1：

#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;
}

例题4-12-2：

#include<stdio.h>
int main(void)
{int child,men,women;for(men=0;men<=15;men++)for(women=0;women<=22;women++){child=45-women-men;if(men*3+women*2+child*0.5==45)printf("men=%d,women=%d,child=%d\n",men,women,child);}return 0;
}