C Primer Plus（第6版）第四章答案

1.

#include <stdio.h>

int main (void)
{
    char a[80], b[80];

    printf ("Enter your first name: ");
    scanf ("%s", a);
    printf ("Enter your last name: ");
    scanf ("%s", b);
    printf ("%s, %s", b, a);

    return 0;
}

2.

#include <stdio.h>
#include <string.h>

int main (void)
{
    char a[80];
    int length;

    printf ("Enter your name: ");
    scanf ("%s", a);
    printf ("\"%s\"\n", a);
    printf ("\"%20s\"\n", a);
    printf ("\"%-20s\"\n", a);
    length = strlen(a) + 3;
    printf ("%*s", length, a);

    return 0;
}

3.

#include <stdio.h>

int main (void)
{
    float a;

    printf ("Enter a floating-number: ");
    scanf ("%f", &a);
    printf ("input is %.1f, or %.1e\n", a, a);
    printf ("input is %.3f, or %.3E", a, a);

    return 0;
}

4.

#include <stdio.h>

int main (void)
{
    float height;
    char name[20];

    printf ("Please input your height: \n");
    scanf ("%f", &height);
    printf ("Please input your name: \n");
    scanf ("%s", name);

    printf ("%s, you are %.3f feet of feet tall", name, height);

    return 0;
}

5.

#include <stdio.h>

int main (void)
{
    float speed, size;

    printf ("Please input speed in Mb/s: \n");
    scanf ("%f", &speed);
    printf ("Please input size in MB: \n");
    scanf ("%f", &size);

    printf ("At %.2f megabits per second, a file of %.2f megabytes downloads in %.2f seconds.", speed, size, (size * 8) / speed);

    return 0;
}

6.

#include <stdio.h>
#include <string.h>

int main (void)
{
    char last[20], first[20];
    int a, b;

    printf ("Please input your first name:\n");
    scanf ("%s", first);
    printf ("Please input your last name:\n");
    scanf ("%s", last);
    a = strlen (first);
    b = strlen (last);

    printf ("%s %s\n", first, last);
    printf ("%*d %*d\n", a, a, b, b);
    printf ("%s %s\n", first, last);
    printf ("%*d %*d", -a, a, -b, b);

    return 0;
}

7.

#include <stdio.h>
#include <float.h>

int main (void)
{
    double a = 1.0 / 3.0;
    float b = 1.0 / 3.0;

    printf ("%.6f, %.6f\n", a, b);
    printf ("%.12f, %.12f\n", a, b);
    printf ("%.16f, %.16f\n", a, b);
    printf ("%d, %d", FLT_DIG, DBL_DIG);

    return 0;
}

8.

#include <stdio.h>
#define a 3.785
#define b 1.609

int main (void)
{
    float mile, gallon;

    printf ("Please input miles and gallons:\n");
    scanf ("%f %f", &mile, &gallon);
    printf ("Miles per gallon: %.1f\n", mile / gallon);
    printf ("Litres per 100 kilometres: %.1f", gallon * a / (mile * b) * 100);

    return 0;
}