过程抽象和返回一个值的函数(例子代码)

//3.1函数调用//r根据用户的预算，计算可以购买多大的狗舍//#include<iostream>#include<cmath>#include<stdlib.h>using namespace std;int main(){const double COST_PER_SQ_FT = 10.50;double budget,area,length_side;cout << "Enter the amout budgeted for your dog house $";cin >> budget;area=budget/COST_PER_SQ_FT;length_side=sqrt(area);cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<"For a price of $"<<budget<<endl<<"I can build you a luxurious square dog house/n"<<"that is "<<length_side<<" feet on each sibe./n";system("pause");return 0;}

前些天一直不晓得cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2); 是干什么用的，今天终于查到了：setf()是追加标志字的函数,而flags()是设置标志字；fixed标志是以定点形式显示浮点数；showpoint标志是强制显示小数点；precision就是精度，表示输出多少小数位。

——2010.12.4

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 // 3.3函数的定义//#include<iostream>#include<stdlib.h>using namespace std;double total_cost(int number_par,double price_par);//函数声明，计算以单价price_par购买number_par件商品的总价，含5%税销售int main(){double price,bill;int number;cout<<"Enter the number of items purchased: ";cin>>number;cout<<"Enter the price per item $";cin>>price;bill=total_cost(number,price);//函数调用cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<number<<" items at "<<"$"<<price<<" each./n"<<"Final bill,including tax,is $"<<bill<<endl;system("pause");return 0;}double total_cost(int number_par,double price_par){const double TAX_RATE=0.05;//5%税额double subtotal;subtotal=price_par*number_par;return(subtotal+subtotal*TAX_RATE);}

——2010.12.5

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 //3.5实参顺序有错//判断用户的成绩，要么为Pass(及格)，要么为Fail(不及格)#include<iostream>#include<stdlib.h>using namespace std;char grade(int received_par,int min_score_par);//如果received_par大于或等于min_score_par,返回'P'表示及格；//否则返回'F'表示不及格int main(){int score,need_to_pass;char letter_grade;cout<<"Enter your score and the minimum needed to pass:/n";cin>>score>>need_to_pass;letter_grade=grade(need_to_pass,score);//注意形参顺序cout<<"You received a score of "<<score<<endl<<"Minimum to pass is "<<need_to_pass<<endl;if(letter_grade=='P'){cout<<"You passed. Congratulation!/n";}else{cout<<"Sorry.You failed./n";}cout<<letter_grade<<" will be entered in your record./n";system("pause");return 0;}char grade(int received_par,int min_score_par){if(received_par>=min_score_par){return 'P';}else{return 'F';}}

——2010.12.6

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//3.9购买比萨//判断两种比萨哪一种最适合购买#include<iostream>#include<stdlib.h>using namespace std;double unitprice(int diameter,double price);//返回比萨每平方英寸的价格//形参diameter是以英寸为单位的比萨直径，形参price是比萨的价格int main(){int diameter_small,diameter_large;double price_small,unitprice_small,price_large,unitprice_large;cout<<"Welcome to the Pizza Consumers Union./n";cout<<"Enter diameter of a small pizza (in inches):";cin>>diameter_small;cout<<"Enter the price of a small pizz: $";cin>>price_small;cout<<"Enter diameter of a large pizza (in inches):";cin>>diameter_large;cout<<"Enter the price of a large pizz: $";cin>>price_large;unitprice_small=unitprice(diameter_small,price_small);unitprice_large=unitprice(diameter_large,price_large);cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<"Small pizza:/n"<<"Diameter= "<<diameter_small<<endl<<"Price= $"<<price_small<<" Per square inch= $"<<unitprice_small<<endl<<"Large pizza:/n"<<"Diameter= "<<diameter_large<<endl<<"Price= $"<<price_large<<" Per square inch= $"<<unitprice_large<<endl;if(unitprice_large<unitprice_small){cout<<"The large one is the better buy./n";}else{cout<<"The small one is the better buy./n";}cout<<"Buon Appetito!/n";system("pause");return 0;}double unitprice(int diameter,double price){const double PI=3.14159;double radius,area;radius=diameter/static_cast<double>(2); //强制类型转换保证结果精度和正确性area=PI*radius*radius;return(price/area);}

//3.10局部变量//计算一块豌豆试验田的平均收成#include<iostream>#include<stdlib.h>using namespace std;double est_total(int min_peas,int max_peas,int pod_count);//返回预计收获的豌豆总数//形参pod_count是豆荚数//形参min_peas和max_peas是每个豆荚中的最少和最多豌豆数int main(){int max_count,min_count,pod_count;double average_pea,yield; //这里average_pea为main的局部变量cout<<"Enter minimum and maximum number of peas in a pod: ";cin>>min_count>>max_count;cout<<"Enter the number of pods: ";cin>>pod_count;cout<<"Enter the weight of an average pea (in ounces): ";cin>>average_pea;yield=est_total(min_count,max_count,pod_count)*average_pea;cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<"Min number of peas per pod= "<<min_count<<endl<<"Max number of peas per pod= "<<max_count<<endl<<"Pod count = "<<pod_count<<endl<<"Average pea weight= "<<average_pea<<" ounces"<<endl<<"Estimated average yield= "<<yield<<" ounces"<<endl;system("pause");return 0;}double est_total(int min_peas,int max_peas,int pod_count){double average_pea;//这里average_pea为est_total的局部变量average_pea=(max_peas+min_peas)/2.0;return(pod_count*average_pea);}

——2010.12.8

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//3.11一个全局命名常量//计算一个圆的面积和一个球体的体积.//两个计算使用同样的半径#include<stdlib.h>#include<iostream>#include<cmath>using namespace std;const double PI=3.14159;double area(double raqius);//返回具有指定半径的一个圆的面积double volume(double radius);//返回具有指定半径的一个球的体积int main(){double radius_of_both,area_of_circle,volume_of_sphere;cout<<"Enter a radius to use for both a circle and a sphere(in inches): /n";cin>>radius_of_both;area_of_circle=area(radius_of_both);volume_of_sphere=volume(radius_of_both);cout<<"Radius= "<<radius_of_both<<" inches/n"<<"Area of circle= "<<area_of_circle<<" square inches/n" //圆的面积单位是平方英寸<<"Volume of sphere= "<<volume_of_sphere<<" cubic inches/n";//球体的体积单位是立方英寸system("pause");return 0;}double area(double radius){return(PI*pow(radius,2));//PI全局常量}double volume(double radius){return((4.0/3.0)*PI*pow(radius,3));//PI全局常量}

——2010.12.9

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//3.12形参作用局部变量//律师事务所计费程序#include<iostream>#include<stdlib.h>using namespace std;const double RATE=150.00; //每刻钟收费double fee(int hours_worked,int minutes_worked);//返回hours_worked小时又minutes_worked分钟的律师费int main(){int hours,minutes;double bill;cout<<"Welcome to the offices of Dewey,Cheatham,and Howe./n"<<"The law office with a heart./n"<<"Enter the hours and minutes of your consultation:/n";cin>>hours>>minutes;bill=fee(hours,minutes);cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<"For "<<hours<<" hours and "<<minutes//minutes的值没有被fee函数调用更改<<" minutes,your bill is $"<<bill<<endl;system("pause");return 0;}double fee(int hours_worked,int minutes_worked)//minutes_worked被初始化为minutes的值{int quarter_hours;minutes_worked=hours_worked*60+minutes_worked;quarter_hours=minutes_worked/15;return(quarter_hours*RATE);}

 

//3.13使用命名空间//计算一个圆的面积和一个球体的体积//两个计算使用相同的半径#include<iostream>#include<stdlib.h>#include<cmath>const double PI=3.14159;double area(double radius);//返回具有指定半径的一个圆的面积double volume(double radius);//返回具有指定半径的一个球的体积int main(){using namespace std;//局部使用double radius_of_both,area_of_circle,volume_of_sphere;cout<<"Enter a radius to use for both a circle and a sphere(in inches): /n";cin>>radius_of_both;area_of_circle=area(radius_of_both);volume_of_sphere=volume(radius_of_both);cout<<"Radius= "<<radius_of_both<<" inches /n"<<"Area of circle= "<<area_of_circle<<" square inches/n"<<"Volume of sphere= "<<volume_of_sphere<<" cubic inches/n";system("pause");return 0;}double area(double radius){using namespace std;//局部使用return(PI*pow(radius,2));}double volume(double radius){using namespace std;//局部使用return((4.0/3.0)*PI*pow(radius,3));}

 

//3.15重载一个函数名称//演示对函数名称ave的重载#include<iostream>#include<stdlib.h>double ave(double n1,double n2);//返回两个数字n1和n2的平均值double ave(double n1,double n2,double n3);//返回三个数字n1,n2,n3的平均值int main(){using namespace std;cout<<"The average of 2.0,2.5 and 3.0 is "<<ave(2.0,2.5,3.0)<<endl;//这的ave()函数带3个参数cout<<"The average of 4.5 and 5.5 is "<<ave(4.5,5.5)<<endl;//这的ave()函数带2个参数system("pause");return 0;}double ave(double n1,double n2)//这的ave()函数带2个参数{return((n1+n2)/2.0);}double ave(double n1,double n2,double n3)//这的ave()函数带3个参数{return((n1+n2+n3)/3.0);}

 

//3.16重载函数名称//判断圆形比萨和矩形比萨，哪一种更适合购买#include<iostream>#include<stdlib.h>double unitprice(int diameter,double price);//返回圆形比萨每平方英寸的价格，形参diameter是以英寸为单位//的比萨直径，形参price是比萨的价格double unitprice(int length,int width,double price);//返回矩形比萨每平方英寸的价格//比萨的长度和宽度分别是length英寸和width英寸//形参price是比萨的价格int main(){using namespace std;int diameter ,length,width;double price_round,unit_price_round,price_rectangular, unitprice_rectangular;cout<<"Wlecome to the Pizza Consumers Union./n";cout<<"Enter the diameter in inches of a round pizza: ";cin>>diameter;cout<<"Enter the price of a round pizza: $";cin>>price_round;cout<<"Enter length and width in inches of a rectangular pizza: ";cin>>length>>width;cout<<"Enter the price of a rectangular pizza: $";cin>>price_rectangular;//重载unitprice函数的使用unitprice_rectangular=unitprice(length,width,price_rectangular);unit_price_round=unitprice(diameter,price_round);cout.setf(ios::fixed);cout.setf(ios::showpoint);cout.precision(2);cout<<endl<<"Round pizza: Diameter= "<<diameter<<" inches/n"<<"Price= $"<<price_round<<" Per square inch= $"<<unit_price_round<<endl<<"Rectangular pizza: Length= "<<length<<" inches/n"<<"Rectangular pizza: Width= "<<width<<" inches/n"<<"Price= $"<<price_rectangular<<" Per square inch= $"<<unitprice_rectangular<<endl;if(unit_price_round<unitprice_rectangular){cout<<"The round one is the better buy./n";}else{cout<<"The rectangular one is the better buy./n";}cout<<"Buon Appetito!/n";system("pause");return 0;}double unitprice(int diameter,double price){const double PI=3.14159;double radius,area;radius=diameter/static_cast<double>(2);area=PI*radius*radius;return(price/area);}double unitprice(int length,int width,double price){double area=length*width;return(price/area);}

——2010.1210

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