CODE EXAMPLE FOR CSHARP

convert a string to an integer without using library

public static void Main() {
    string str = Console.ReadLine();
    int j = 0;
    int myNumber = 0;
    string strReverse =String.Empty;

    //Reverse the string
    foreach (char temp in str)
    {
        strReverse = temp + strReverse;
    }

    foreach (char temp in strReverse)
    {
        int i = temp - 48; //Ascii character
        myNumber = myNumber + i * myPower(10,j);
        j++;
    }
    Console.WriteLine(myNumber);
    Console.ReadLine();
}


public static int myPower(int i, int j)
{
    int final = 1;
    for (int loop =0 ; loop < j; loop++)
        final = final  * i;
    return final;
}