C Primer Plus（第6版）第六章答案

1.

#include <stdio.h>int main (void){    int num = 26;    int i;    char letter[26];    char ch = 'a';    for (i = 0; i < num; i++, ch++)    {        letter[i] = ch;    }    for (i = 0; i < 26; i++)    {        printf ("%c\n", letter[i]);    }    return 0;}

2.

#include <stdio.h>int main (void){    int i, j;    for (i = 1; i <= 5; i++)    {        for (j = 1; j <= i; j++)        {            printf ("$");        }        printf ("\n");    }    return 0;}

3.

#include <stdio.h>int main (void){    int i, j;    for (i = 1; i <= 6; i++)    {        char l = 'F';        for (j = 1; j <= i; j++, l--)        {            printf ("%c", l);        }        printf ("\n");    }    return 0;}

4.

#include <stdio.h>int main (void){    int i, j;    char l = 'A';    for (i = 1; i <= 6; i++)    {        for (j = 1; j <= i; j++, l++)        {            printf ("%c", l);        }        printf ("\n");    }    return 0;}

5.

#include <stdio.h>int main (void){    int i, j;    char ch;    printf ("Enter a letter: ");    scanf ("%c", &ch);    for (i = 0; i <= ch - 'A' + 1; i++)    {        for (j = 0; j < ch - 'A' + 1 - i; j++)        {            printf (" ");        }        for (j = 0; j <= i; j++)        {            printf ("%c", 'A' + j);        }        for (j = i - 1; j >= 0; j--)        {            printf ("%c", 'A' + j);        }        printf ("\n");    }    return 0;}

6.

#include <stdio.h>void print (int min, int max);int main (void){    int low, high;    printf ("Enter the min and max:\n");    scanf ("%d %d", &low, &high);    print (low, high);    return 0;}void print (int min, int max){    int i;    for (i = min; i <= max; i++)    {        printf("%d %d %d\n", i, i * i, i * i * i);    }    return;}

7.

#include <stdio.h>#include <string.h>int main (void){    char str[20];    int max;    int i;    printf ("Enter a word:\n");    scanf ("%s", str);    max = strlen (str) - 1;    for (i = max; i >= 0; i--)        printf ("%c", str[i]);    return 0;}

8.

#include <stdio.h>int main (void){    double min, max;    printf ("Enter two numbers:\n");    while (scanf ("%lf %lf", &min, &max) == 2)    {        printf ("%lf\n", (min - max > 0 ? min - max : max - min) / (min * max));        printf ("Enter two numbers:\n");    }    return 0;}

9.

#include <stdio.h>double cal (double min, double max);int main (void){    double min, max;    printf ("Enter two numbers:\n");    while (scanf ("%lf %lf", &min, &max) == 2)    {        printf ("%lf\n", cal (min, max));        printf ("Enter two numbers:\n");    }    return 0;}double cal (double min, double max){    return (min - max > 0 ? min - max : max - min) / (min * max);}

10.

#include <stdio.h>int add (int min, int max);int main (void){    int min, max;    printf ("Enter lower and upper integer limits: ");    while ((scanf ("%d %d", &min, &max)) == 2)    {        if (min >= max)            break;        printf ("The sum of the squares from %d to %d is %d\n", min * min, max * max, add (min, max));        printf ("Enter lower and upper integer limits: ");    }    printf ("Done");    return 0;}int add (int min, int max){    int i;    int sum = 0;    for (i = min; i <= max; i++)        sum += i * i;    return sum;}

11.

#include <stdio.h>int main (void){    int in[8];    int i;    printf ("Enter 8 numbers: ");    for (i = 0; i < 8; i++)        scanf ("%d", &in[i]);    for (i = 7; i >= 0; i--)        printf ("%d\n", in[i]);    return 0;}

12.

#include <stdio.h>float add1 (int num);float add2 (int num);int main (void){    int num;    printf ("Enter the number: ");    scanf ("%d", &num);    printf ("%f", add1 (num) + add2 (num));    return 0;}float add1 (int num){    int i;    float sum = 0.0;    for (i = 1; i <= num; i++)        sum += 1.0 / i;    return sum;}float add2 (int num){    int i;    float sum = 0.0;    int j = -1;    for (i = 1; i <= num; i++)    {        j *= -1;        sum += (1.0 / i) * j;    }    return sum;}

13.

#include <stdio.h>#include <math.h>int main (void){    int in[8];    int i;    for (i = 0; i < 8; i++)        in[i] = pow (2, i);    i = 0;    do    {        printf ("%d\n", in[i]);        i++;    }    while (i < 8);    return 0;}

14.

#include <stdio.h>int main (void){    double a[8], b[8];    int i, j;    printf ("Enter 8 numbers: ");    for (i = 0; i < 8; i++)    {        scanf ("%lf", &a[i]);        for(j = 0, b[i] = 0; j <= i; j++)            b[i] += a[j];    }    for (i = 0; i < 8; i++)        printf ("%8lf  ", a[i]);    printf ("\n");    for (i = 0; i < 8; i++)        printf ("%8lf  ", b[i]);    return 0;}

15.

#include <stdio.h>#include <string.h>int main (void){    char str[255];    int num;    int i;    scanf ("%s", str);    num = strlen (str) - 1;    for (i = num; i >= 0; i--)        printf ("%c", str[i]);    return 0;}

16.

#include <stdio.h>double de (int num);double da (int num);int main (void){    int num = 1;    while (de (num) <= da (num))        num++;    printf ("year: %d\nDeirdre: %lf\nDaphne: %lf", num, de (num), da (num));    return 0;}double de (int num){    double sum = 100.0;    int i;    for (i = 1; i <= num; i++)        sum *= 1.05;    return sum;}double da (int num){    double sum = 100.0;    int i;    for (i = 1; i <= num; i++)        sum += 100.0 * 0.1;    return sum;}

17.

#include <stdio.h>int main (void){    int year = 0;    double sum = 100.0;    while (sum > 0)    {        sum *= 1.08;        sum -= 10.0;        year++;    }    printf ("%d", year);    return 0;}

18.

#include <stdio.h>int main (void){    int i = 1;    int f = 5;    while (f < 150)    {        f = (f - i) * 2;        printf ("week %d: friends: %d\n", i, f);        i++;    }    return 0;}