Why my code miscalculates conversions?

You can see my progress below. I'm so confused because when I try to calculate 0C to K, my code perfectly calculates 1F to K. I couldn't check other wrong answers but probably I messed up those if/elseif statements. I'm not looking for the working code so study sources are welcome too.

prompt={'Enter temperature','Enter unit of temperature (C, F or K)','Enter unit of temperature wanted (C, F or K'};
dlgtitle='Temperature Converter CFK';
dims = [1 1 1];
user_input=inputdlg(prompt,dlgtitle,dims);
if strcmp(user_input{2},'C')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'F')
    t1f=((t1*(9/5))+32);
end
if strcmp(user_input{2},'C')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'K')
    t1f=(t1+273.15);
end
if strcmp(user_input{2},'F')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'C')
    t1f=((t1-32)*(5/9));
end
if strcmp(user_input{2},'F')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'K')
    t1f=(((t1-32)*(5/9))+273.15);
end
if strcmp(user_input{2},'K')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'C')
    t1f=(t1-273.15);
end
if strcmp(user_input{2},'K')
    t1= str2double(user_input{1});
elseif strcmp(user_input{3},'F')
    t1f=(((t1-273.15)*(9/5))+32);
end
msgbox ([num2str(t1f) , user_input{3}])

Answer 1

[Walter Roberson]

if strcmp(user_input{2},'C')
    t1= str2double(user_input{1});

That statement is executed any time the second input is 'C'

elseif strcmp(user_input{3},'F')
    t1f=((t1*(9/5))+32);

That statement is only executed if the second input is not C but the third input is F

You want more like

    if strcmp(user_input{2},'C') && strcmp(user_input{3},'F')

[Les Beckham]

Yes. And this line should appear only once above the if tests:

t1= str2double(user_input{1});

with only t1f being calculated inside the if tests.

[Emir]

Thank you both for your answers. Mr. Robertson's answer solved my issue. Mr. Beckham your notification probably saved me a couple points because it was already like what you suggest, but I made it up like this while trying to bugfix the code. I'll send this page's link to my professor to let him know how I solved the bug which I informed earlier.