C Primer Plus（第6版）第四章答案

#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;
}

#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;
}

#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;
}

#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;
}

#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;
}

#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;
}

#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;
}

#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;
}