What is the term used for a number that is written into a program’s code?

C# Visual Studio

In your own words, answer all questions :
1- Write a code example uses string concatenation.
2-What is the term used for a number that is written into a program’s code? Write a code example that assigns this term to a variable.
3-What are the two arguments that you pass to a TryParse method? What is the purpose of each argument? Provide a code example using TryParse.
4-Write a code example that uses a nested decision structure to perform the following: if amount1 is greater than 10 and amount2 is less than 100, display the greater of amount1 and amount2.
Ch4- Assume nameListbox is a Listbox control. Write code that reads the selected item from the ListBox. Be sure to prevent an exception from occurring in case no item has been selected.