4.1.c

#include <stdio.h>

int main(void) {
	
	char first_name[20], last_name[20];
	printf("Please enter your first name.\n");
	scanf("%s", first_name);
	printf("Please enter your last name.\n");
	scanf("%s", last_name);
	printf("%s,%s", first_name, last_name);
	
	return 0;
}

4.2.c

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

int main(void) {
	
	char first_name[20], last_name[20];
	printf("Please enter your first name.\n");
	scanf("%s", first_name);
	printf("Please enter your last name.\n");
	scanf("%s", last_name);
	
	printf("a: \"%s %s\"\n", first_name, last_name);
	printf("b: \"%20s %20s\"\n", first_name, last_name);
	printf("c: \"%-20s %-20s\"\n", first_name, last_name);
	
	int lenght_first, lenght_last;
	lenght_first = strlen(first_name);
	lenght_last = strlen(last_name);
	printf("d: %*s %*s", lenght_first, first_name, lenght_last, last_name);
	
	return 0;
}

4.3.c

#include <stdio.h>

int main(void) {
	
	double number;
	printf("Please enter a float number.\n");
	scanf("%lf", &number);
	
	printf("a: %.1f  %.1e\n", number, number);
	printf("b: %.3f  %.3E\n", number, number);
	
	return 0;
}

4.4.c

#include <stdio.h>

int main(void) {
	
	float height;
	char name[20];
	
	printf("Please enter your height(in inches).\n");
	scanf("%f", &height);
	printf("Please enter your name.\n");
	scanf("%s", name);
	
	printf("%s, you are %.3f feet tall", name, height);
	
	return 0;
}

4.5.c

#include <stdio.h>

int main(void) {
	
	float speed;
	float bytes;
	
	printf("What's speed when you download(Mb/s)?\n");
	scanf("%f", &speed);
	printf("How large is the file size(MB)?\n");
	scanf("%f", &bytes);
	printf("At %.2f megabits per second, a file of %.2f megabytes download in %.2f seconds\n",
		speed, bytes, (bytes * 8) / speed);
	
	return 0;
} 

4.6.c

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

int main(void) {
	
	char first_name[20], last_name[20];
	int lenght_first, lenght_last;
	
	printf("Please enter your first name.\n");
	scanf("%s", first_name);
	printf("Please enter your last name.\n");
	scanf("%s", last_name);
	
	lenght_first = strlen(first_name);
	lenght_last = strlen(last_name);
	
	printf("%*s %*s\n", lenght_first, first_name, lenght_last, last_name);
	printf("%*d %*d\n", lenght_first, lenght_first, lenght_last, lenght_last);
	printf("%*s %*s\n", lenght_first, first_name, lenght_last, last_name);
	printf("%-*d %-*d\n", lenght_first, lenght_first, lenght_last, lenght_last);
	
	return 0;
}

4.7.c

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

int main(void) {
	
	double number1 = 1.0 / 3.0;
	float number2 = 1.0 / 3.0;
	
	printf("*%.6lf*\n*%.12lf*\n*%.16lf*\n", number1, number1, number1);
	printf("*%.6f*\n*%.12f*\n*%.16f*\n", number2, number2, number2);
	printf("FLT_DIG = %d\n", FLT_DIG);
	printf("DBL_DIG = %d\n", DBL_DIG);

	
	return 0;
}

4.8.c

#include <stdio.h>
#define PER_GALLONS 3.785
#define PER_KM 1.609

int main(void) {
	
    const double MILES = 3.785;	
	double mileage;
	double gasoline;
	
	printf("Enter the mileage and the amount of gasoline consumed.\n");
	scanf("%lf %lf", &mileage, &gasoline);
	printf("Consumed one gasoline oil can drive %.1f miles.\n", mileage / gasoline);
	printf("Translate in rise/km: %.1f", (gasoline * PER_GALLONS) / (PER_KM * mileage * 100));
	
	return 0;
 }