我正在尝试在C ++中创建一个用户定义函数，以防止无限循环为双变量输入错误的输入，并检查输入是否为负或零。如果是这种情况，该函数将进入do-while循环，要求用户重试，直到该值不再是双精度，负数或零之外。
功能fix（）是用户定义的
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
string fix(double x)
{
string B_error = "B cannot be zero or negative. Please try again: ";
string H_error = "H cannot be zero or negative. Please try again: ";
string h_error = "b cannot be zero or negative. Please try again: ";
string b_error = "h cannot be zero or negative. Please try again: ";
string r_error = "r cannot be zero or negative. Please try again: ";
string y_error;
while (!(cin >> x))
{
if (cin.fail())
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not an integer
cin.ignore(10000, '\n');
}
}
if (x == 'B')
{
y_error = B_error;
if (x <= 0)
{
do
{
return y_error;
cin >> x;
}
while (x <= 0);
}
}
return 0;
}
int main()
{
int selection;
double I, B, H, b, h, r, fix(double);
cout << "Please select the type of beam:\n"
<< "1) I-Beam\n"
<< "2) Rectangular Beam\n"
<< "3) Cylindrical Beam\n";
while (!(cin >> selection) || selection < 1 || selection > 3)
{
if (cin.fail() || selection < 1 || selection > 3)
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not an integer
cin.ignore(10000, '\n');
}
}
switch (selection)
{
case 1:
cout << "You have selected I-beam. All inputs must be in inches.\n"
<< "Please input the value for B: ";
fix(B);
cout << "Please input the value for H: ";
fix(H);
if (H <= 0)
{
do
{
cout << "H cannot be zero or negative. Please try again: ";
cin >> H;
}
while (H <= 0);
}
cout << "Please input the value for b: ";
fix(b);
if (b <= 0)
{
do
{
cout << "b cannot be zero or negative. Please try again: ";
cin >> b;
}
while (b <= 0);
}
else if (b > B)
{
do
{
cout << "b cannot be larger than B. Please try again: ";
cin >> b;
}
while (b > B);
}
cout << "Please input the value for h: ";
fix(h);
if (h <= 0)
{
do
{
cout << "h cannot be zero or negative. Please try again: ";
cin >> h;
}
while (h <= 0);
}
else if (h > H)
{
do
{
cout << "h cannot be larger than H. Please try again: ";
cin >> H;
}
while (h > H);
}
I = (B*H*H*H - b*h*h*h)/12.;
cout << "\nResults for an I-beam with B = " << B
<< ", H = " << H << ", b = " << b << ", and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 2:
cout << "You have selected rectangular beam. All inputs must be in inches.\n"
<< "Please input the value for b: ";
fix(b);
if (b <= 0)
{
do
{
cout << "b cannot be zero or negative. Please try again: ";
cin >> b;
}
while (b <= 0);
}
cout << "Please input the value for h: ";
fix(h);
if (h <= 0)
{
do
{
cout << "h cannot be zero or negative. Please try again: ";
cin >> h;
}
while (h <= 0);
}
I = b*h*h*h/12.;
cout << "\nResults for a rectangular beam with b = " << b << " and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 3:
cout << "You have selected cylindrical beam. All inputs must be in inches.\n"
<< "Please input the value of r: ";
fix(r);
if (r <= 0)
{
do
{
cout << "r cannot be zero or negative. Please try again: ";
cin >> r;
}
while (r <= 0);
}
I = M_PI*pow(r,4)/4.;
cout << "\nResults for a cylindrical beam with r = " << r << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
}
cout << "The value of the moment of inertia for this beam is: " << I << "in^4" << "\n\n";
return 0;
}
我删除了这些问题。您正在将类的实例与函数混淆。函数不必初始化，实例必须在类之外。我在代码中写了一些注释。它仍然不是很漂亮，但至少可以正常工作。
string FUNCTION(double)顺便说一句。表示该函数只能或应该返回“字符串”。如果不返回任何内容，则该函数的编写方式如下void FUNCTION(double)。如果您退货一个字符串，您必须编写一些可以接收返回的字符串的内容，例如：
#include <iostream>
/*
std::string returning_value;
returning_value = FUNCTION(1.0);
*/
//or
std::string FUNCTION(double function_a); //prototype of the function
//you need this if you write the function underneath the main() function
//The main function is returning "return 0" so since "0" is an "int"
//meaning main is always "int main()" btw. because it is a function,
//just not some function but the "main function" thats called by the OS
int main()
{
std::string returning_value;
double a = 0.1; //initializing with 0.1
returning_value = FUNCTION(a);
std::cout << returning_value << std::endl;
//and in both cases the function would look like:
return 0;
}
std::string FUNCTION(double function_a)
{
std::string returning_value_a = "This is a string that will be returned";
if(function_a == 0.1)
{
returning_value_a = "This is another string";
}
return returning_value_a;
}
您的固定金额最少的代码至少可以正常工作您可以测试如何获得想要的正确输出。玩得开心:)希望我的回答对您有所帮助：）
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
void fix(double x)
{
string B_error = "B cannot be zero or negative. Please try again: ";
string H_error = "H cannot be zero or negative. Please try again: ";
string h_error = "b cannot be zero or negative. Please try again: ";
string b_error = "h cannot be zero or negative. Please try again: ";
string r_error = "r cannot be zero or negative. Please try again: ";
string y_error;
while (!(cin >> x))
{
if (cin.fail())
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not an integer
cin.ignore(10000, '\n');
}
}
//warning: comparing floating point with == or != is unsafe
if (x == 'B')
{
y_error = B_error;
if (x <= 0)
{
do
{
cin >> x;
}
while (x <= 0);
}
}
}
int main()
{
int selection;
double I, B, H, b, h, r;
//You need to initialize the variables with a value
I = 1.0;
B = 1.0;
H = 1.0;
b = 1.0;
h = 1.0;
r = 1.0;
//functions don't need to be initialized, thats for Instanzes of classes
//double fix(double);
cout << "Please select the type of beam:\n"
<< "1) I-Beam\n"
<< "2) Rectangular Beam\n"
<< "3) Cylindrical Beam\n";
while (!(cin >> selection) || selection < 1 || selection > 3)
{
if (cin.fail() || selection < 1 || selection > 3)
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not an integer
cin.ignore(10000, '\n');
}
}
switch (selection)
{
case 1:
cout << "You have selected I-beam. All inputs must be in inches.\n"
<< "Please input the value for B: ";
fix(B);
cout << "Please input the value for H: ";
fix(H);
if (H <= 0)
{
do
{
cout << "H cannot be zero or negative. Please try again: ";
cin >> H;
}
while (H <= 0);
}
cout << "Please input the value for b: ";
fix(b);
if (b <= 0)
{
do
{
cout << "b cannot be zero or negative. Please try again: ";
cin >> b;
}
while (b <= 0);
}
else if (b > B)
{
do
{
cout << "b cannot be larger than B. Please try again: ";
cin >> b;
}
while (b > B);
}
cout << "Please input the value for h: ";
fix(h);
if (h <= 0)
{
do
{
cout << "h cannot be zero or negative. Please try again: ";
cin >> h;
}
while (h <= 0);
}
else if (h > H)
{
do
{
cout << "h cannot be larger than H. Please try again: ";
cin >> H;
}
while (h > H);
}
I = (B*H*H*H - b*h*h*h)/12.;
cout << "\nResults for an I-beam with B = " << B
<< ", H = " << H << ", b = " << b << ", and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 2:
cout << "You have selected rectangular beam. All inputs must be in inches.\n"
<< "Please input the value for b: ";
fix(b);
if (b <= 0)
{
do
{
cout << "b cannot be zero or negative. Please try again: ";
cin >> b;
}
while (b <= 0);
}
cout << "Please input the value for h: ";
fix(h);
if (h <= 0)
{
do
{
cout << "h cannot be zero or negative. Please try again: ";
cin >> h;
}
while (h <= 0);
}
I = b*h*h*h/12.;
cout << "\nResults for a rectangular beam with b = " << b << " and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 3:
cout << "You have selected cylindrical beam. All inputs must be in inches.\n"
<< "Please input the value of r: ";
fix(r);
if (r <= 0)
{
do
{
cout << "r cannot be zero or negative. Please try again: ";
cin >> r;
}
while (r <= 0);
}
I = M_PI*pow(r,4)/4.;
cout << "\nResults for a cylindrical beam with r = " << r << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
}
cout << "The value of the moment of inertia for this beam is: " << I << "in^4" << "\n\n";
return 0;
}
所以，我不得不添加另一个函数来检查B
这是我的修正代码：
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
void fix(double &x)
{
while (!(cin >> x))
{
if (cin.fail())
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not a double
cin.ignore(10000, '\n');
}
}
string return_x = "This cannot be zero or negative. Please try again: ";
while (x <= 0)
{
cout << return_x << endl;
cin >> x;
}
}
void fix2(double &x, double &y)
{
while (x < y)
{
cout << x << " cannot be less than " << y << endl;
fix(y);
}
}
int main()
{
int selection;
double I = 1.0;
double B = 1.0;
double H = 1.0;
double b = 1.0;
double h = 1.0;
double r = 1.0;
cout << "Please select the type of beam:\n"
<< "1) I-Beam\n"
<< "2) Rectangular Beam\n"
<< "3) Cylindrical Beam\n";
while (!(cin >> selection) || selection < 1 || selection > 3)
{
if (cin.fail() || selection < 1 || selection > 3)
{
cout << "Erroneous input. Please try again:\n";
cin.clear(); // used to prevent an endless loop if an input type is not an integer
cin.ignore(10000, '\n');
}
}
switch (selection)
{
case 1:
cout << "You have selected I-beam. All inputs must be in inches.\n"
<< "Please input the value for B: ";
fix(B);
cout << "Please input the value for H: ";
fix(H);
cout << "Please input the value for b: ";
fix(b);
fix2(B, b);
cout << "Please input the value for h: ";
fix(h);
fix2(H, h);
I = (B * H * H * H - b * h * h * h) / 12.;
cout << "\nResults for an I-beam with B = " << B << ", H = " << H
<< ", b = " << b << ", and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 2:
cout << "You have selected rectangular beam. All inputs must be in inches.\n"
<< "Please input the value for b: ";
fix(b);
cout << "Please input the value for h: ";
fix(h);
I = b * h * h * h / 12.;
cout << "\nResults for a rectangular beam with b = " << b
<< " and h = " << h << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
case 3:
cout << "You have selected cylindrical beam. All inputs must be in inches.\n"
<< "Please input the value of r: ";
fix(r);
I = M_PI * pow(r, 4) / 4.;
cout << "\nResults for a cylindrical beam with r = " << r << endl;
cout << setfill('-') << setw(32) << "" << endl;
break;
}
cout << "The value of the moment of inertia for this beam is: " << I
<< "in^4" << "\n\n";
return 0;
}