Trying to use a for loop to calculate years with an IF statement but it seems to ignore it.

Question

Chett Manly 2021-9-13

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https://ww2.mathworks.cn/matlabcentral/answers/1452419-trying-to-use-a-for-loop-to-calculate-years-with-an-if-statement-but-it-seems-to-ignore-it

评论： Chett Manly 2021-9-14

So the program is meant to stop if balance >= 500000 but it seems to soldier on until it runs out of months. Use of a for loop is required.

clear; close all; clc

balance(1) = 1000;

contribution = 1200;

M = 1; % month ticker

years = 12/M;

interest = 0.0025;

for M = 1:300

if balance(M) >= 50000 %balance(M)

end

M = M + 1; % you need to increment months + 1 every cycle

balance(M) = balance(M-1) + interest*balance(M-1) + contribution;

end

%Balance %This will display the final Balancefprintf('%g Months until $500000 reached\n', M);

fprintf('%g Years until $500000 reached\n', years);

12 Years until $500000 reached

format bank

plot(balance);

grid on

ytickformat('usd')

title('Saving 3% compound')

xlabel('Months')

ylabel('Saving balance')

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Answer 1

Jan 2021-9-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1452419-trying-to-use-a-for-loop-to-calculate-years-with-an-if-statement-but-it-seems-to-ignore-it#answer_786524

编辑：Jan 2021-9-13

在 MATLAB Online 中打开

Either

for M = 2:300
    if balance(M) >= 50000 %balance(M)
        break;  % Leave the for M loop
    end
    % NOPE ! M = M + 1; % you need to increment months + 1 every cycle
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;
end

or

for M = 2:300
    if balance(M) < 50000 %balance(M)
       % NOPE ! M = M + 1; % you need to increment months + 1 every cycle
       balance(M) = balance(M-1) + interest*balance(M-1) + contribution;
    end
end

If you do not know in advanve how log a loop runs, a while loop is nicer:

M = 2;
while M <= 300 && balance(M) < 50000
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;
    M = M + 1;
end

While the counter M must be increased in the while loop, this is done in the for loop automatically.

[EDITED] M starts at 2 now.

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Jan 2021-9-13

在 MATLAB Online 中打开

This looks strange:

M = 1; % month ticker
years = 12/M;  % Are you sure that 12/1 is the number of years?!
               % The usual definition is Months / 12
for M = 1:300
    if balance(M) >= 500000 %balance(M)
        break;  % Leave the for M loop
    end
    % No! Do not increase the loop counter inside the
    % body of a FOR loop:
    %   M = M + 1;    

My code failed, because accessing balance(M - 1) requires the loop to start at M=2. I've edited my answer.

Label = max(balance) is not useful before the loop, because balance contains 1 value only.

Chett Manly 2021-9-14

在 MATLAB Online 中打开

You were right about the year ticker, it needs to be lower in the code to work correctly.

If you disable the M line in the loop, and change the for if argument to not have the M ticker the program.

This version runs but if I change the M value to 2 and the for arguement to 2:300 then it won't run.

clear; close all; clc
balance(1) = 1000;
contribution = 1200;
M = 1; % month ticker
interest = 0.0025;
for M = 1:300
    if balance(M) >= 500000 %balance(M)
        break;  % Leave the for M loop
    end
     M = M + 1; % you need to increment months + 1 every cycle
    balance(M) = balance(M-1) + interest*balance(M-1) + contribution;
    Label = max(balance) %this labels the plot with max balance
end
%Balance %This will display the final Balancefprintf('%g Months until $500000 reached\n', M);
years = M/12;
fprintf('%g Years until $500000 reached\n', years);
format bank
plot(balance);
grid on
ytickformat('usd')
title('Saving 3% compound')
xlabel('Months')
ylabel('Saving balance')
%This creates the Label on the plot
txt = {'Max Balance:',Label,'\leftarrow'};
text(M,Label,txt,'HorizontalAlignment','right')