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Понял. Вот три программы без комментариев и с английским текстом ввода/вывода.

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Task 1

```cpp
#include <iostream>
using namespace std;

int main() {
    int n;
    cout << "Enter array size: ";
    cin >> n;

    int arr[100];

    cout << "Enter " << n << " elements: ";
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
    }

    int sum = 0;
    for (int i = 0; i < n; i += 2) {
        sum += arr[i];
    }

    cout << "Sum of elements at even positions: " << sum << endl;

    return 0;
}
```

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Task 2

```cpp
#include <iostream>
using namespace std;

int main() {
    int rows, cols;
    cout << "Enter number of rows and columns: ";
    cin >> rows >> cols;

    int matrix[100][100];

    cout << "Enter matrix elements:" << endl;
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            cin >> matrix[i][j];
        }
    }

    int col1, col2;
    cout << "Enter two column numbers to swap (1-based): ";
    cin >> col1 >> col2;

    col1--;
    col2--;

    for (int i = 0; i < rows; i++) {
        int temp = matrix[i][col1];
        matrix[i][col1] = matrix[i][col2];
        matrix[i][col2] = temp;
    }

    cout << "Matrix after swap:" << endl;
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            cout << matrix[i][j] << "\t";
        }
        cout << endl;
    }

    return 0;
}
```

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Task 3

```cpp
#include <iostream>
using namespace std;

int main() {
    char str[256];

    cout << "Enter a string: ";
    cin.ignore();
    cin.getline(str, 256);

    char result[256];
    int j = 0;

    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] != ' ') {
            result[j] = str[i];
            j++;
        }
    }
    result[j] = '\0';

    cout << "String without spaces: " << result << endl;

    return 0;
}
```