C primer plus第七章习题

复习题很轻松的通过了，不赘述了。
最近工作开始忙了，第七章看的效果很慢，但是兴趣还在上了24小时的班之后居然能兴致勃勃的写代码，当做休息吧。
瞎扯结束，以上。

编程练习

1.

/很简单，看会书上例题就可以。/
#include

2.

#include <stdio.h>int main(void){    char ch;    int n;    for( n = 1;ch = getchar() != '#';n++)    {        printf("%c %d", ch, ch);        if(n%8==0)            printf("\n");    }    return 0;}

3.

#include <stdio.h>int main(void){    int a = 0, b = 0, c = 0, d = 0, i;    printf("Please enter the number:\n");    while(1)    {        scanf("%d", & i);        if(i == 0)            break;        if(i%2==0)            {                a++;                b += i;            }        else             {                c++;                d += i;            }    }    printf("%d %d %d %d", a, b/a, c, d/c);    return 0;}

变量名依然取不好。while（1）可以无限循环，直到输入0，break这个循环。做错的原因是用了getchar…….用顺手了………

4.

#include <stdio.h>int main(void){    char ch;    int a,b;    while((ch = getchar()) != '#')    {        if(ch == '.')        {            putchar('!');            a++;        }        else if(ch == '!')        {            putchar('!');            b++;        }        else            putchar(ch);    }    printf("%d times . to !", a);    printf("%d times ! to !!", b);    return 0;}

putchar（”）需要注意。

5.

#include <stdio.h>int main(void){    int num, odd = 0, even = 0, sum_odd = 0, sum_even = 0;    printf("Plese enter the number:\n");    while(1)    {        scanf("%d", &num);        if(num == 0)            break;        switch(num % 2 != 0)        {        case 1: sum_odd += num;                odd++;                break;        case 0: sum_even += num;                even++;        }    }    printf("odd count is %d.\n", sum_odd);    printf("odd average is %d.\n", sum_odd / odd);    printf("even count is %d.\n", sum_even);    printf("even count is %d.\n", sum_even / even);    return 0;}

6.

#include <stdio.h>int main(void){    int count = 0;    char first = 0,second ;    while((second = getchar()) != '#')    {        if((first == 'e') && (second == 'i'))            count++;            first = second;    }    printf("'ei' appeared %d times.\n", count);    return 0;}

7.

#include <stdio.h>#define HOURPER 100#define TAX1 0.15#define TAX2 0.2#define TAX3 0.25int main(void){     float pay, hours, tax;    printf("Please enter the hours:\n");    scanf("%f", &hours);    if(hours > 40.0 )    {        hours = 40 + (hours - 40) *1.5;        pay = hours * HOURPER;        printf("Pay is %f.\n", pay);    }    else            pay = hours * HOURPER;    if(pay <= 300)        tax = pay * TAX1;    else if(pay <= 450)        tax = 300 * TAX1 + (pay - 300) * TAX2;    else        tax = 300 * TAX1 + 150 * TAX2 + (pay - 450) * TAX3;     printf("pay is %f,tax is %f, income is %f\n", pay, tax, pay - tax);    return 0;}

8.

#include <stdio.h>#define TAX1 0.15#define TAX2 0.2#define TAX3 0.25int main(void){     float pay, hours, tax, HOURPER;    while(1)    {        printf("Enter the number corresponding to the desired pay rate or action:\n");        printf("1) $8.75/hr\t\t\t2) $9.33/hr\n");        printf("3) $10.00/hr\t\t\t4) $11.20/hr\n");        printf("5) quit\n");        switch(get_int())        {            case 1: HOURPER = 8.75;                    break;            case 2: HOURPER = 9.33;                    break;            case 3: HOURPER = 10.00;                    break;            case 4: HOURPER = 11.20;                    break;            case 5: printf("quit.\n");                    return 0;        }        printf("Pleas enter the hours:\n");        scanf("%f", &hours);        if(hours > 40.0 )        {            hours = 40 + (hours - 40) *1.5;            pay = hours * HOURPER;            printf("Pay is %f.\n", pay);        }        else                pay = hours * HOURPER;        if(pay <= 300)            tax = pay * TAX1;        else if(pay <= 450)            tax = 300 * TAX1 + (pay - 300) * TAX2;        else            tax = 300 * TAX1 + 150 * TAX2 + (pay - 450) * TAX3;         printf("pay is %f,tax is %f, income is %f\n", pay, tax, pay - tax);        return 0;    }}int get_int(void){    int num;    char str[40];    while(scanf("%d", &num) != 1)    {        gets(str);        printf("Please enter the NUMBER!\n");    }    while(getchar() != '\n');    return num;}

定义了一个get_int函数，用来过滤非法选择的数字，得到1到5的选择整数。

9.

#include <stdio.h>int isprimer(int);int main(void){    int num,i;    printf("please enter a positive number:\n");    scanf("%d", &num);    for(i=2;i<=num;i++)        if(isprimer(i))            printf("%d\t", i);    printf("\n");    return 0;}int isprimer(int n){    int div;    for(div =2; div * div <=n; div++)        if(n % div == 0)            return 0;    return 1;}

isprimer（）是判断素数的函数（记不住就多看，多记几遍），素数返回1，非素数返回0。

10.