Here is an example C++ program that reads data from a CSV file, stores it in an array, performs some manipulation, and writes the result to a text file: 

#include 
#include 
#include 
#include 
#include 

using namespace std;

int main() {

    // Open CSV file for reading
    ifstream inputFile("data.csv");

    // Check if file opened successfully
    if (!inputFile.is_open()) {
        cout << "Error: could not open file." << endl;
        return 1;
    }

    // Read data from CSV file
    vector<vector> data;
    string line;
    while (getline(inputFile, line)) {
        stringstream ss(line);
        vector row;
        string value;
        while (getline(ss, value, ',')) {
            row.push_back(stod(value));
        }
        data.push_back(row);
    }

    // Close CSV file
    inputFile.close();

    // Perform some manipulation on data
    for (int i = 0; i < data.size(); i++) {
        data[i][0] += 1.0;
        data[i][1] *= 2.0;
    }

    // Open output file for writing
    ofstream outputFile("result.txt");

    // Check if file opened successfully
    if (!outputFile.is_open()) {
        cout << "Error: could not open file." << endl;
        return 1;
    }

    // Write manipulated data to output file
    for (int i = 0; i < data.size(); i++) {
        for (int j = 0; j < data[i].size(); j++) {
            outputFile << data[i][j] << " ";
        }
        outputFile << endl;
    }

    // Close output file
    outputFile.close();

    return 0;
}

In this example, the CSV file to be read is named data.csv, and the output file to be written is named result.txt. The program reads the CSV data into a vector of vectors, where each inner vector represents a row of the CSV data. The program then performs some manipulation on the data (adding 1 to the first column and multiplying the second column by 2), and writes the manipulated data to the output file in text format, with each row separated by a newline character.