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 1.609int 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;}