如何在 c++ 中正确从正整数中获取偶数和奇数？

How to get even & odd numbers correctly from a positive integer in c++?

本文关键字：获取 c++ 整数      更新时间：2023-10-16

我是C++新手...我无法从正整数中获取偶数和奇数。但由于某种原因，它无法正确显示它。因此，在我的 if-else 语句中，我使用mod运算符，并使用偶数even = even * 10 + remainder;，而我试图做的奇数是：odd = odd * 10 + remainder;..我收到错误

二进制表达式的操作数无效。

所以，任何人都可以通过从正整数中获取偶数和奇数来帮助我解决问题。谢谢。

这是我的代码：

#include <iostream>
#include <fstream> // for file stream. 

using namespace std;
int main() {
// Variables 
int x, reversedNumber, remainder;
// Creating String variables and setting them to empty string. 
string even = "", odd = "";
// Creating a file. 
ofstream out;
out.open("outDataFile.txt");
// creating a character variable 
// for the user input if they want to use the program again. 
char ch;
do {
// Even number. 
even = "";
// Odd number.
odd = "";
// Reversed number
reversedNumber = 0;
// Prompt the user to enter a positive integer. 
cout << "nEnter a positive integer and press <Enter> ";

// Validate user input. 
//        if (cin >> x && x < 0) {
//
//        } else {
//             cout << "Invalid entry, Try again." << endl;
//            cin.clear();
//            while (cin.get() != 'n');  
//        }
// Display Results to the screen
cout << "the original number is " << x << "n";
// Display results in the text file. 
out << "the original number is " << x << "n";
// Display number reversed. 
cout << "the number reversed ";
// Display number reversed in text file. 
out << "the number reversed ";
//Reversing the integer. 
while (x != 0) {
remainder = x % 10;
reversedNumber = reversedNumber * 10 + remainder;
// Display on screen 
cout << remainder << " ";
// Display in text file. 
out << remainder << " ";
x /= 10;
}
// Display the results on screen and in the text file. 
cout << "n";
out << "n";

// Reading the reverse numbers result.
while (reversedNumber != 0) {
remainder = reversedNumber % 10;

// Checking if the number is even or odd. 
if (remainder % 2 == 0) {
// even = even * 10 + remainder;

} else  {

//  odd = odd * 10 + remainder;

}
reversedNumber /= 10;
}
//Displaying the even numbers. 
if (even != "") {
cout << "the even digits are " << even << "n";

out << "the even digits are " << even << "n";

}          
// If it is not even then display.. 
else {
cout << "There are no even digits n";
out << "There are no even digits n";
}
//Display the odd results. 
if (odd != "") {
cout << "the odd digits are " << odd << "n";
out << "the odd digits are " << odd << "n";
}           
// If its not odd then display. 
else {
cout << "There are no odd digits n";
out << "There are no odd digits n";
}
// just a divider to divide the results inside text file.
out << "----------------- n";
// Prompt the user if they want to use the program again.
cout << "nDo you like to continue/repeat? (Y/N):";
// get the input from user. 
cin >> ch;
if ((ch == 'Y') || (ch == 'y')) {
} else {
cout << "nGoodbye!" << endl;
}
} while (ch == 'y' || ch == 'Y');

// close the text file. 
out.close();
return 0;
}

在将数字附加到字符串之前将其转换为字符串：

while (reversedNumber != 0) {
remainder = reversedNumber % 10;
// Checking if the number is even or odd. 
if (remainder % 2 == 0) {
even += std::to_string(remainder);    
} else  {
odd += std::to_string(remainder);
}
reversedNumber /= 10;
}

如果您对使用std::to_string感到不舒服，那么您可以将even和odd作为整数，只需执行以下操作：

int even = 0;
int odd = 0;
...
while (reversedNumber != 0) {
remainder = reversedNumber % 10;
// Checking if the number is even or odd. 
if (remainder % 2 == 0) {
even *= 10 + remainder;    
} else  {
odd *= 10 + remainder;
}
reversedNumber /= 10;
}
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