c prime plus 第六版 第四章课后编程答案（vscode编写）

4-1 

#include <stdio.h>
int main(void)
{
    char xing[30],ming[30];    
    scanf("%s%s",ming,xing);
    printf("%s,%s\n",ming,xing);
    return 0;

}

4-2

#include <stdio.h>
#include <string.h>
int main(void)
{
    int a,b;
    char xing[30],ming[30];    
    scanf("%s%s",ming,xing);
    a = strlen(ming) + 3;
    b = strlen(xing) + 3;
    printf("\"%s\" \"%s\"\n",ming,xing);
    printf("\"%20s\" \"%20s\"\n",ming,xing);  
    printf("\"%-20s\" \"%-20s\"\n",ming,xing);
    printf("\"%*s\" \"%*s\"\n",a,ming,b,xing);
    return 0;
}

4-3

#include <stdio.h>
int main (void)
{
    float a;
    scanf("%f",&a);
    printf("%f\n",a);
    printf("%e\n",a);

    return 0;
}

4-4

#include <stdio.h>
int main(void)
{
    char name[40];
    float height;  
    scanf("%f",&height);
    scanf("%s",name);
    printf("%s,you are %f feet tall\n",name,height / 100);
    return 0;
}

4-5

#include <stdio.h>

int main(void)
{
    float speed, size;

    printf("Please enter net speed(Mb/s): ");
    scanf("%f", &speed);
    printf("Please enter file size(MB): ");
    scanf("%f", &size);
    printf("At %.2f megabits per second, ", speed);
    printf("a file of %.2f megabytes\n", size);
    printf("downloads in %.2f seconds.\n", size * 8 / speed);

    return 0;
}

4-6

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

int main(void)
{
    int x, y;
    char fname[20], lname[20];

    printf("Please enter your first name: ");
    scanf("%19s", fname);
    printf("Please enter your last name: ");
    scanf("%19s", lname);
    x = strlen(fname);
    y = strlen(lname);
    printf("%s %s\n", fname, lname);
    printf("%*d %*d\n", x, x, y, y);
    printf("%s %s\n", fname, lname);
    printf("%-*d %-*d\n", x, x, y, y);

    return 0;
}

4-7

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

int main(void)
{
    float f_value = 1.0 / 3.0;
    double d_value = 1.0 / 3.0;

    printf("1.0 / 3.0 display 6 decimal places:\n");
    printf("f_value = %.6f\nd_value = %.6lf\n", f_value, d_value);

    printf("\n1.0 / 3.0 display 12 decimal places:\n");
    printf("f_value = %.12f\nd_value = %.12lf\n", f_value, d_value);

    printf("\n1.0 / 3.0 display 16 decimal places:\n");
    printf("f_value = %.16f\nd_value = %.16lf\n", f_value, d_value);

    printf("\nfloat and double maximum precious digits:\n");
    printf("FLT_DIG = %d, DBL_DIG = %d\n", FLT_DIG, DBL_DIG);
    //4.8-7书上问答: 不一致, 因为float精确度是6位, 而double是15位, 所以在超过精确度位数后会有差异 

    return 0;
}

4-8

#include <stdio.h>
#define GALLON_TO_LITRE 3.785
#define MILE_TO_KM 1.609

int main(void)
{
    double range, oil;

    printf("Please input the range you traveled(in mile): ");
    scanf("%lf", &range);
    printf("Please input the oil you spend(in gallon): ");
    scanf("%lf", &oil);

    printf("Fuel consumptions:\n");
    printf("In USA, your oil wear is %.1f mile / gallon.\n", range / oil);
    printf("In Europe, your oil wear is ");
    printf("%.1f litre / 100km.\n", 100.0 * (oil * GALLON_TO_LITRE) / (range * MILE_TO_KM));

    return 0;
}