why my graph doesnt start at 0, and how to fix it?

old_balance = 2000;
monthly_contri = 200;
monthly_interest = 0.06/12;
new_balance = zeros(1,216);
new_balance(1) = old_balance;
yearly_balance = zeros(1,18);
month=0;
for i=1:216
    new_balance(i+1) = new_balance(i) + (new_balance(i) * monthly_interest) + monthly_contri;
end
total_savings = new_balance(216);
for i=1:18
    month = month+12;
    yearly_balance(i)= new_balance(month);
end
 
yearly_tution = zeros(1,18);
tut_rate = 0.0575;
prog_selc = input('Select a program: 1. Arts; 2. Science; 3.Engineering: ');
switch prog_selc
    case 1
       art(1) = 6000;
       for i = 1:22
           art(i+1) = art(i) + (art(i) * tut_rate);
       end
       tution = sum(art(19:22));
       for i = 1:18
       yearly_tution(i) = tution;
       end
    case 2
       sci(1) = 6500;
       for i = 1:22
           sci(i+1) = sci(i) + (sci(i) * tut_rate);
       end
       tution = sum(sci(19:22));
       for i=1:18
       yearly_tution(i) = tution;
       end
    case 3
        engg(1) = 7000;
        for i = 1:22
            engg(i+1)= engg(i) + (engg(i) * tut_rate);
        end
        tution = sum(engg(19:22));
        for i = 1:18
        yearly_tution(i) = tution;
        end
end

fprintf('At the end of 18 years you will have saved $ %6.2f\n',total_savings);
fprintf('The cost of a 4-year college tution fee is $ %6.2f\n',tution);

if total_savings >= tution
    disp('Congratulations!!!! You have saved enough.');
elseif tution > total_savings
    short = tution - total_savings;
    fprintf('The saving is $ %6.2f short.\n',short);
end

years=1:18;
plot(years,yearly_tution,'-b',years,yearly_balance,'-g')
title('College Savings vs. Tution fee')
xlabel('Year')
ylabel('Balance')

Answer 1

[Cris LaPierre]

Which axis is supposed to start at 0? X or Y?

X is years. That does not start at 0 because you define it to start at 1:

years=1:18;

For the blue line, Y is yearly_tuition. You define a non-zero value for art(1), sci(1) and engg(1). You then add to it in the for loop, and then set every value of yearly_tuition equal to the sum of values 19-22.

For the green line, Y is the yearly_balance. You assign in a value from new_balance. The first value of new_balance is old_balance (2000), and then you add to it in the first for loop.

old_balance = 2000;
...
new_balance(1) = old_balance;