Read input from a file, capitalize first letter, make every other letter lowercase, and output into a separate file

Question

I am supposed to ask the user for two file names (input and output files). The contents from the input file should be read and the first letter of each sentence should be made u

Answer 1

You have a minor logical error.

You first need to check, if the character is a period. This state you need to remember. If then a next character isalpha, then we check, if recently the newsentence flag has been set. In this case, and only in this case, we reset the new sentence flag and convert the character to uppercase.

All other alpha characters will be converted to lowercase. Other charcaters will not be converted.

In your solution you always reset the newsentence flag. Even, if the next print character is a space (Which is most liekly the case).

Please see updated solution:

#include 
#include 
#include 
#include 
using namespace std;

int main() {
    string input_file;  // To hold input file name
    string output_File; // To hold output file name
    char ch;            // To hold character
    fstream inputFile;
    fstream outputFile;

    bool new_sentence = true;

    cout << "Enter input file name: " << endl;
    cin >> input_file;

    cout << "Enter output file name: " << endl;
    cin >> output_File;

    outputFile.open(output_File, ios::out);
    inputFile.open(input_file, ios::in);

    if (inputFile) {
        while (inputFile.get(ch)) {
            if (ch == '.') {
                new_sentence = true;
            }
            if (isalpha(ch)) {
                if (new_sentence) {
                    ch = toupper(ch);
                        new_sentence = false;
                }
                else {
                    ch = tolower(ch);
                }
            }
            outputFile.put(ch);
        }
        inputFile.close();
        outputFile.close();
    }
    else {
        cout << "Cannot open file(s)." << endl;
}

    cout << "\nFile conversion complete." << endl;

    return 0;
}

And then, please see some further improvements:

#include 
#include 
#include 
#include 


int main() {
    // Will hold the input and output filename
    std::string filename;  

    // This is our flag to indicate that a new sentence will come
    bool newSentence = true;

    // Get input filename
    std::cout << "Enter input file name: " << "\n";
    std::cin >> filename;
    // And try to open the file
    std::ifstream inFile(filename);

    std::cout << "Enter output file name: " << "\n";
    std::cin >> filename;
    // And try to open the file
    std::ofstream outFile(filename);

    // Only convert, if the input and output file could be opened 
    if (inFile && outFile) {
        char ch;
        while (inFile.get(ch)) {
            if (ch == '.') {
                newSentence = true;
            }
            if (isalpha(ch)) {
                if (newSentence) {
                    ch = toupper(ch);
                    newSentence = false;
                }
                else {
                    ch = tolower(ch);
                }
            }
            outFile.put(ch);
        }
    }
    else {
        std::cout << "Cannot open file(s)\n";
    }
    std::cout << "\nFile conversion program complete\n";
    return 0;
}

And the full blown "C++ with algorithm" solution. Here the conversion, or transformation is done in one statement

#include 
#include 
#include 
#include 
#include 
#include 

int main() {
    // Will hold the input and output filename
    std::string filename;  

    // Get input filename
    std::cout << "Enter input file name: " << "\n";
    std::cin >> filename;
    // And try to open the file
    std::ifstream inFile(filename);

    std::cout << "Enter output file name: " << "\n";
    std::cin >> filename;
    // And try to open the file
    std::ofstream outFile(filename);

    // Only convert, if the input and output file could be opened 
    if (inFile && outFile) {
        // Do the conversion
        std::transform(
            std::istreambuf_iterator(inFile), 
            std::istreambuf_iterator(),
            std::ostreambuf_iterator(outFile),
            [newSentence = true](char c) mutable {
                if (c == '.') newSentence = true; 
                if (std::isalpha(c)) 
                    if (newSentence) { 
                        newSentence = false; 
                        c = std::toupper(c); }  
                    else c = std::tolower(c); 
                return c;
            }
        );
    }
    else {
        std::cout << "Cannot open file(s)\n";
    }
    std::cout << "\nFile conversion program complete\n";
    return 0;
}

But if the last solution adds additional value? I am not sure . . .