C++ 函数程序中的平均输出始终为 0.0

Average output in c++ functions program is always 0.0

本文关键字：输出 函数 程序 C++      更新时间：2023-10-16

我正在编写一个程序，使用函数计算三个温度的平均值，由于某种原因，我的输出始终为 0.0。我不确定它是否与代码中变量的位置有关，或者我是否应该初始化其中的至少一个，但事实是我似乎无法找出问题所在。我对编程以及涉及函数和对象的编程仍然很陌生。我在这里缺少什么吗？

void getTemps(double);
double calcAvg(double tempAvg);
void displayAvg();
double temp1, temp2, temp3;
double sum;
float tempAvg;
int main()
{
getTemps(sum);
calcAvg(tempAvg);
displayAvg();
system("PAUSE");
return 0;
}
void getTemps(double sum)
{
// Get up to three temperatures
cout << "Enter temperatures of 3 cities." << endl;
cin >> temp1;
cin >> temp2;
cin >> temp3;
sum = temp1 + temp2 + temp3;
}
double calcAvg(double tempAvg)
{
tempAvg = (sum / 3);
return tempAvg;
}
void displayAvg()
{
cout << fixed << setprecision(1) << temp1 << endl;
cout << fixed << setprecision(1) << temp2 << endl;
cout << fixed << setprecision(1) << temp3 << endl;
cout << "The average temperature is " << tempAvg << " degrees." << endl;
}

#include <iomanip>
#include <iostream>
using namespace std;
/*
If you want to change the variable values that you pass into this function
then you will need to pass by reference using "&" when declaring the function 
params. See below:
*/
void getTemps(double & sum, double &temp1, double & temp2, double & temp3);
/*
You don't need to change the sum variable so I DONT pass the sum by 
reference here.
*/
double calcAvg(double & tempAvg, double sum);
/*
You do not need to alter any of the variables in this function, so just pass
them without the ref or with a const tag so you don't end up accidentally
altering them.
*/
void displayAvg(double tempAvg, double temp1, double temp2, double temp3);
//You should place these variables in the main method and then pass them to your functions.
//double temp1, temp2, temp3;
//double sum;
//float tempAvg;
int main(){
double temp1, temp2, temp3;
double sum;
double tempAvg; //I changed this variable to a double becuase all of your functions deal with doubles and your other variables are doubles.
//All of these variables are now passed by reference, 
//so they will be altered when you change them in the function.
getTemps(sum, temp1, temp2, temp3);
calcAvg(tempAvg, sum);
displayAvg(tempAvg, temp1, temp2, temp3);
system("PAUSE");
return 0;
}
void getTemps(double & sum, double &temp1, double & temp2, double & temp3){
// Get up to three temperatures
cout << "Enter temperatures of 3 cities." << endl;
cin >> temp1;
cin >> temp2;
cin >> temp3;
sum = temp1 + temp2 + temp3;
}
double calcAvg(double & tempAvg, double sum){
tempAvg = (sum / 3);
return tempAvg;
}
void displayAvg(double tempAvg, double temp1, double temp2, double temp3){
cout << fixed << setprecision(1) << temp1 << endl;
cout << fixed << setprecision(1) << temp2 << endl;
cout << fixed << setprecision(1) << temp3 << endl;
cout << "The average temperature is " << tempAvg << " degrees." << endl;
}

发生这种情况是因为您将全局变量发送到函数调用。因此，在您的函数中创建此变量的副本。如果你想使用全局变量，答案是：

void getTemps();
void calcAvg();
void displayAvg();
double temp1, temp2, temp3;
double sum;
float tempAvg;
int main()
{
getTemps();
calcAvg();
displayAvg();
cin.get();
cin.get();
//system("PAUSE");
return 0;
}
void getTemps()
{
// Get up to three temperatures
cout << "Enter temperatures of 3 cities." << endl;
cin >> temp1;
cin >> temp2;
cin >> temp3;
sum = temp1 + temp2 + temp3;
}
void calcAvg()
{
tempAvg = (sum / 3);

}
void displayAvg()
{
cout << fixed /*<< setprecision(1)*/ << temp1 << endl;
cout << fixed /*<< setprecision(1)*/ << temp2 << endl;
cout << fixed /*<< setprecision(1*/ << temp3 << endl;
cout << "The average temperature is " << tempAvg << " degrees." << endl;
}

但这是一种糟糕的编程风格。 会更好：

#include<iostream>
using namespace std;
double getTemps(double& temp1, double& temp2, double& temp3);
double calcAvg(const double sum);
void displayAvg(const double temp1, const double temp2, const double temp3, const double tempAvg);

int main()
{
double sum=0;
double temps1=0.f, temps2=0.f,temps3=0.f;
double tempavg = 0.f;
sum=getTemps(temps1,temps2,temps3);
tempavg=calcAvg(sum);
displayAvg(temps1,temps2,temps3,sum);
cin.get();
cin.get();
//system("PAUSE");
return 0;
}
double getTemps(double& temp1, double& temp2, double& temp3)
{
// Get up to three temperatures
cout << "Enter temperatures of 3 cities." << endl;
cin >> temp1;
cin >> temp2;
cin >> temp3;
return   (temp1 + temp2 + temp3);
}
double calcAvg(const double sum)
{

return (sum / 3);
}
void displayAvg(const double temp1, const double temp2, const double temp3, const double tempAvg)
{
cout << fixed /*<< setprecision(1)*/ << temp1 << endl;
cout << fixed /*<< setprecision(1)*/ << temp2 << endl;
cout << fixed /*<< setprecision(1*/ << temp3 << endl;
cout << "The average temperature is " << tempAvg << " degrees." << endl;
}
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