问移位解密工具(塞萨尔密码)

EN

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>

using namespace std;
const int ARRAYSIZE = 128;

void characterCount(char ch, int list[]);
void calcShift( int& shift, int list[]);
void writeOutput(ifstream &in, ofstream &out, int shift);

int main()
{
    int asciiCode = 0,
        shift = 0;
    string filename;
    char ch;
    ifstream infile;
    ofstream outfile;

    //input file

    cout << "Input file name: ";
    getline(cin, filename);

    infile.open(filename.c_str());

        if (!infile.is_open()) { 

            cout << "Unable to open file or it doesn't exist." << endl;

            return 1;

        }

    //output file

    cout << "Output file name: ";
    getline(cin, filename);



    outfile.open(filename.c_str());

    int list[ARRAYSIZE] = {0}; 

        while (infile.peek() != EOF) 
        {
            infile.get(ch);
            characterCount(ch, list); 
        }



    infile.clear();
    infile.seekg(0);

    calcShift (shift, list); //Calculate the shift based on the <strong class="highlight">most</strong> characters counted
    writeOutput(infile, outfile, shift); //Decypher and write to the other document

    return 0;
}

void characterCount(char ch, int list[])
{
        if (ch >= 'A' && ch <= 'z') //If the character is in the alphabet...
        {
            int asciiCode = 0;

            asciiCode = static_cast<int>(ch); //Change it to the ASCII number
            list[asciiCode]++; //And note it on the array
        }
}

void calcShift( int& shift, int list[])
{
    int maxIndex = 0, //Asuming that list[0] is the largest
        largest = 0;

        for (int i = 1; i < ARRAYSIZE; i++)
        {
            if (list[maxIndex] < list[i])
                    maxIndex = i; //If this is true, change the largest index
        }

    largest = list[maxIndex]; //When the maxIndex is found, then that has the largest number.

        if (largest >= 65 && largest <= 90) //Calculate shift with <strong class="highlight">E</strong> (for upper-case letters)
            shift = largest - 69;

        if (largest >= 97 && largest <= 122) //For lower-case letters (<strong class="highlight">e</strong>)
            shift = largest - 101;
}

void writeOutput(ifstream &infile, ofstream &outfile, int shift)
{
    char ch;
    int asciiCode = 0;

        while (infile.peek() != EOF) { //Until it is the end of the file...

            infile.get(ch); //Get the next character

                if (ch >= 'A' && ch <= 'z') //If the character is in the alphabet...
                {
                    asciiCode = static_cast<int>(ch); //Change it to the ASCII number
                    asciiCode += shift; //Do the shift
                    ch = static_cast<char>(asciiCode); //Change it to the shifted letter
                }

            outfile << ch; //Print to the outfile
        }
}