4章

/* 判断正整数m是否为素数 */
#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!=!)
        printf("%d is a prime number!\n",m);
    else
        printf("No!\n");



    return 0;
}

/*简单的猜数游戏 */
#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! 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;
}

/* 使用函数计算 1!+2!+3!+...+100!*/
#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;
}
/* 定义求 n! 的函数 */
double fact(int n)
{
    int i;
    double result;


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


    return  result;
}

/* 45人正好搬45块砖， 程序版本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;
}

/* 使用嵌套循环计算 1!+2!+3!+...+100! */
#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;
}<=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;
}

/*  从输入的n个成绩中选出最高分， 用for语句实现  */
#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;
}

/* 逆序输出一个正整数 */
#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;
}

/* 使用嵌套循环求100以内的全部素数 */
#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;
}

/* 输出斐波那契序列： 1,2,3,5,8，...的前10项 */
#include<stdio.h>
int main(void)
{
    int i,x1,x2,x;

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


    return 0;
}

/*  用格雷戈里公式计算π的近似值，精度要求：最后一项的绝对值小于0.0001  */
#include<stdio.h>
#include<math.h>
int main(void)
{
    int denominator,flag;
    double item,pi;


    /* 循环初始化 */
    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;
}


         

/* 输入一批学生的成绩， 以负数作为结束标志， 计算平均成绩， 并统计不及格人数 */
#include<stdio.h>
int main(void)
{
    int count,num;
    double grade,total;
    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;
}

        

/* 统计一个整数的位数 */
#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;
}