[英]C++ Writing to file
程序应该以这种形式写入用户输入和等效于文件“output.txt”的罗马数字1984: MCMLXXXIV这是原始用户输入和转换函数的结果。 在我的文本文件中,我在文件成功创建的 txt 文档上只得到“0:”。 代码如下。
#include <iostream>
#include <string>
#include <iomanip>
#include <fstream>
using namespace std;
string convert(int digit, string low, string mid, string high);
void saveToFile(int &, string[], const int &);
int main()
{
const int MAX_INPUT = 3999, MIN_INPUT = 1, // These constants hold high and low integer numbers,
ARRAY_SIZE = 4; // and the array size declarator.
string answers[ARRAY_SIZE] = { "", "", "", "" }; //An array of string to hold the output from the convert function.
int accumulator = 0; // Variable to hold number of arabic numbers converted.
int userNum = 0; // Variable to hold user input.
saveToFile(userNum, answers, ARRAY_SIZE);
do { //Main loop - ensures repeated execution until negative entered.
cout << "Enter a negative number to end the program.\n";
cout << "Enter an arabic number between 1 and 3999: ";
accumulator++;
while (!(cin >> userNum) || (userNum < MIN_INPUT || userNum > MAX_INPUT)){ //input validation - only proceed with
if (userNum < 0) //valid, in-range input.
{
cout << "Program Ending due to user request.";
cout << endl << "Arabic numbers converted: " << accumulator - 1 << endl; //Counter
cout << "Thank you for using the program. Have a nice day!" << endl;
system("PAUSE");
exit(EXIT_SUCCESS); //Termintaion with message and exit function
}
else {
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n'); //handling of non-integer input.
cout << "Invalid Value. Number must be between 1 and 3999: ";
}
}
// Digit Extraction - turns userNum into four seperate values
int thous = userNum / 1000; //thousands place value
int hund = userNum % 1000 / 100; //hundreds place value
int tens = userNum % 100 / 10; //tens place value
int ones = userNum % 10 / 1; //ones place value
// filling answers ARRAY OF STRINGS with results from convert function.
answers[0] = convert(thous, "M", "M", "M");
answers[1] = convert(hund, "C", "D", "M");
answers[2] = convert(tens, "X", "L", "C");
answers[3] = convert(ones, "I", "V", "X");
// Printing out equivelent roman numeral on one line.
cout << "\nRoman numeral for " << userNum << " is: ";
cout << answers[0] << answers[1] << answers[2];
cout << answers[3] << endl;
} while (userNum > 0); //Loop to allow multiple numbers per run.
system("PAUSE");
return 0;
}
// Convert function - returns a string for roman numerals broken up by digits, Accepts as arguments
// the extracted digits and three string values known as low, med, and high.
string convert(int digit, string low, string mid, string high)
{
if (digit == 1)
{
return low;
}
if (digit == 2)
{
return low + low;
}
if (digit == 3)
{
return low + low + low;
}
if (digit == 4)
{
return low + mid;
}
if (digit == 5)
{
return mid;
}
if (digit == 6)
{
return mid + low;
}
if (digit == 7)
{
return mid + low + low;
}
if (digit == 8)
{
return mid + low + low + low;
}
if (digit == 9)
{
return low + high;
}
if (digit == 0)
{
return "";
}
}
void saveToFile(int &userNum, string answers[], const int &ARRAY_SIZE)
{
char writeToFile;
cout << "Do you want to write output to a file? Y/N ";
cin >> writeToFile;
if (writeToFile == 89 || writeToFile == 121)
{
ofstream outputFile;
outputFile.open("output.txt");
if (outputFile)
{
outputFile << userNum << ":" << answers[0] + answers[1] + answers[2] + answers[3];
outputFile.close();
}
else
{
cout << "Error opening the file.\n";
exit(EXIT_FAILURE);
}
}
else
return;
}
您在循环之前调用saveToFile
。
您应该在循环结束时调用它:
// Printing out equivalent roman numeral on one line.
cout << "\nRoman numeral for " << userNum << " is: ";
cout << answers[0] << answers[1] << answers[2];
cout << answers[3] << endl;
saveToFile(userNum, answers, ARRAY_SIZE);
} while (userNum > 0);
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