accept two numbers number 1 and number 2 and find the sum of all odd numbers between the two numbers entered

#include <iostream>
using namespace std;


int main()
{
    //a. Prompt the user to input two integers: firstNum and secondNum
    //(firstNum must be less than secondNum).
    cout << "a. Prompt the user to input two integers. First must be less than second\n";
    double firstNum = 2;
    double secondNum = 1;


    while (firstNum > secondNum)
    {
       cout << "enter first number: \n";
       cin >> firstNum;
       cout << "enter second number (must be more than first number): \n";
       cin >> secondNum;


       if (firstNum > secondNum) 
           cout << "first number must be less than second number. Try again. \n";
    }
    cout << "\n";


    //b. Output all odd numbers between firstNum and secondNum.
    cout << "b. Output all odd numbers between firstNum and secondNum.\n";
    int number = firstNum;


    while (number <= secondNum)
    {
        if (number % 2)
            cout << number++ << "\n";
        else
        {
            number++;
            continue;
        }
    }
    cout<<"\n";


    //c. Output the sum of all even numbers between firstNum and secondNum.
    cout << "c. Output the sum of all even numbers between firstNum and secondNum.\n";
    number = firstNum;
    int sum = 0;


    while (number <= secondNum)
    {
        if (!(number % 2))
            sum += number++;
        else
        {
            number++;
            continue;
        }
    }
    cout << "sum = " << sum << "\n\n";


    //d. Output the numbers and their squares between 1 and 10.
    cout << "d.Output the numbers and their squares between 1 and 10.\n";
    number = 1;
    while (number <= 10)
    {
        cout << number << " -> " << number << "^2" << " = " << number * number << '\n';
        number++;
    }
    cout << "\n";


    //e. Output the sum of the square of the odd numbers between firstNum and secondNum.
    cout << "Output the sum of the square of the odd numbers between firstNum and secondNum\n";
    number = firstNum;
    sum = 0;
    while (number <= secondNum)
    {
        if (number % 2)
        {
            sum += (number * number);
            number++;
        }
        else
        {
            number++;
            continue;
        }
    }
    cout << "sum: " << sum << "\n\n";


    //f. Output all uppercase letters.
    cout << "Output all uppercase letters.\n";
    int c = 65;


    while (c < 91)
        cout << char(c++) << ", ";
    cout << "\n";
}