Creating a Spreadsheet using a multidimensional array

I am having trouble with a program, I really don't know how to start. I have to create a simple spreadsheet program that can set values to cells like A1 = 24, and can do operations and put the value of the operations into a cell like C3= A1+2.
The program pretty much calls for the person to make a spread sheet like in excel.
The main problems I have with it is I dunno how write the proper input so I can access certain cells of the array and put information into them, I don't want the program code written so much as I want a basic example on how to take a two dimensional array and be able to access the the elements of the array in program and change the values within those elements so I can type in on the cosole "A1= 3" and have the array element that has A1 in it be changed to 3

So that's several subproblems to work on (and working on subproblems is good, since you can solve one subproblem without worrying about the others at all):
1) Getting input
2) Deciding, given a string, what to do about it (is it an assignment, or a formula, or what)
3) Given a cell reference, how to determine what cell it refers to
4) How to store a formula in your array

Using a two-dimensional array is dead simple: you give the row index and the column index and you're done.

Code:

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int two_d_array[100][100];
two_d_array[5][8] = 4; //set the element in the sixth row and ninth column to 4

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