main函数中如何初始化sum的值？

我想要设计一个公差为1的等差数列求和的函数，且首项与末项可以手动输入。请问main函数中如何初始化sum的值？

#include<iostream>
using namespace std;
int Add(int sum, int val)
{
    int a = 0;
    int b = 0;
    for (int val = a; val <= b; val++)
    {
        sum += val;
        return sum;
    }
}
int main()
{
    int a = 1;
    int b = 10;
    cout << "a=";
    cin >> a;
    cout << "b=";
    cin >> b;
    int val = a;
    int sum=0;
    
    Add(sum, val);
    cout << "sum=" << sum << endl;
    system("pause");
    return 0;
}

修改如下，可对照参考：

 #include<iostream>
using namespace std;
int Add(int a, int b)
{
    int sum=0;
    for (int val = a; val <= b; val++)
    {
        sum += val;
    }
    return sum;
}
int main()
{
    int a = 1;
    int b = 10;
    cout << "a=";
    cin >> a;
    cout << "b=";
    cin >> b;
    cout << "sum=" << Add(a , b) << endl;
    system("pause");
    return 0;
}

运行结果：

有帮助望采纳，谢谢！