3.1

#include<stdafx.h>
#include <iostream>
using namespace std;
const int inch_per_feet = 12;//一英尺（inch）等於12英寸（feet）

int main()

{
	int height,heigh_inch,heigh_feet;
	cout << "enter your height in inch=____\b\b\b\b ";//\b表示退格，與下劃線個數相同，用於指示輸入位置
	cin >> height;
	heigh_inch = height / inch_per_feet;
	heigh_feet = height % inch_per_feet;
	cout << "your height is " << heigh_inch << " inch " << heigh_feet << " feet\n";
	return 0;
}
 

3.2

#include<stdafx.h>
#include <iostream>
using namespace std;
const int inch_per_feet = 12;//一英尺（inch）等於12英寸（feet）
const double feet_per_m = 0.0254;//一英寸等於0.0254米，注意由於後面定義的變數為double型別，這裡宣告也要用double
const double kg_per_pound = 2.2;

int main()

{
	int height_inch, height_feet, weight_pound;//分別表示身高的英尺英寸和體重磅，以整數表示
	double height_m,weight_kg,BMI;//身高米與體重kg以及BMI值都可能為小數，用double型別的變數，注意與前宣告型別保持一致
	//身高體重的輸入
	cout << "enter your heigh in inch:___\b\b";
	cin >> height_inch;
	cout << "enter your heigh in feet:___\b\b";
	cin >> height_feet;
	cout << "enter your weight in pound:___\b\b";
	cin >> weight_pound;
	//身高米、體重kg單位的轉換
	height_m = (height_inch*inch_per_feet + height_inch)*feet_per_m;
	weight_kg = kg_per_pound * weight_pound;
	//BMI值計算
	BMI = weight_kg / (height_m*height_m);//注意這裡的平方不能用^2表示
	cout << "your BMI is " << BMI << endl;
	return 0;
}
 

3.3

#include<stdafx.h>
#include <iostream>
using namespace std;
const int degree_per_minutes = 60;
const int degree_per_second = 60*60;


int main()

{
	double degree, minute, second;
	double latitude;
	cout << "enter a latitude in dgree,minutes,and seconds:\n";
	cout << "First,enter the degrees: ";
	cin >> degree;
	cout << "Next,enter the minutes of arc: ";
	cin >> minute;
	cout << "Finally,enter the second of arc: ";
	cin >> second;
	latitude = degree + minute / degree_per_minutes + second / degree_per_second;//轉換因子與變數至少要有一個為浮點型，否則這個計算結果將會捨去小數部分，導致計算不正確
	cout << degree << "degrees, " << minute << " minutes," << second << " seconds= " << latitude << " degree\n";
	return 0;
}
 

3.4

#include<stdafx.h>
#include <iostream>
using namespace std;
const int day_per_hour = 12;
const int hour_per_minute = 60;
const int minute_per_second = 60;


int main()

{
	long second_origi;//用於輸入秒數
	int day,se_or_d,hour,se_or_h, minute, second;//均定義為int，用於捨去小數
	cout << "enter the number of seconds: ";
	cin >> second_origi;
	day = second_origi / (minute_per_second*hour_per_minute*day_per_hour);
	se_or_d = second_origi - day * (minute_per_second*hour_per_minute*day_per_hour);//存放原始秒數減去天所佔秒數的值，方便計算小時
	hour= se_or_d / (minute_per_second*hour_per_minute);
	se_or_h = se_or_d - hour * hour_per_minute*minute_per_second;//存放剩餘秒數
	minute = se_or_h / minute_per_second;
	second = se_or_h - minute * minute_per_second;
	cout << second_origi << " seconds is " << day << "days, "<<hour<<" hours, "<<minute<<" minutes, "<<second<<" seconds\n";
	return 0;
}

3.5

#include<stdafx.h>
#include <iostream>
using namespace std;
int main()

{
	long long A_p, W_p;
	double rate;
	cout << "enter the world's population: ";
	cin >> W_p;
	cout << "enter the population of the US: ";
	cin >> A_p;
	rate = double (A_p) / W_p * 100;//由於用long long 儲存的變數，必須至少將兩個變數中的一個轉化為浮點型資料，否則求出的比率為0，捨去小數
	cout << "The population of the US is " << rate << "% of the world population";
	return 0;
}

3.6

#include<stdafx.h>
#include <iostream>
using namespace std;
int main()

{
	double distance, A_g, oil_con;//汽油量可能為小數，變數定義為double型別
	cout << "enter the distance in kilometer: ";
	cin >> distance;
	cout <<"enter the amount of gasoline in litre: ";
	cin >> A_g;
	oil_con = A_g/ distance * 100;
	cout << "the oil consumption per 100 kilometers is " << oil_con;
	return 0;
}

3.7

#include<stdafx.h>
#include <iostream>
using namespace std;
const double kilo_100_mile = 62.14;
const double gallon_per_L = 3.875;
int main()

{
	double con_in_Eur,con_in_US;
	cout << "enter the oil consumption in Europe method/100km: ";
	cin >> con_in_Eur;
	con_in_US =kilo_100_mile/con_in_Eur*gallon_per_L;//直接將歐洲風格的耗油量轉換為美國風格的
	cout << "the oil consumption in America style is " << con_in_US << "mpg";
	return 0;
}