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;
}