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====== Math 445 lecture diary: if-elseif-else ======

Today we'll look at slightly more complex functions, with
  * multiple arguments
  * multiple return values
  * ''if-elseif-else'' statements
  * ''switch'' statements

====Multiple arguments and return values====

The declaration of a function ''f'' with multiple arguments and multiple return values has general form
<code matlab>
function [rtn1, rtn2, rtn3, ...] = f(arg1, arg2, arg3, ...)
</code>

====if-elseif-else statement====

The general form of an ''if-elseif-else'' statement is
<code matlab>
if condition1
  action1
elseif condition2
  action2
elseif condition3
  action3
else
  action4
end
</code>
though of course you can have as many ''elseif'' statements as you like.

====Example: if-elseif-else and multiple args and return val====

Write a Matlab function ''temp2kcf'' converts a temperature ''t'' in any one of the three units Kelvin, Celsius, or Farenheit, and returns the temperature in all three units. The function should have two arguments, the temperature ''t'' and a character ''units'' which specifies the units as either K, C, or F and three return values, ''tK, tC, tF''. 

Here's a decent solution to the problem using an ''if-elseif-else'' statement.
<code matlab>
function [tK, tC, tF] = temp2kcf(t, units);
% convert temperature t in units 'C', 'F', or 'K' to all three of those units

  % convert input temp to Kelvin
  if units == 'F'
    tK = 5/9*t + 255.37;
  elseif units == 'C'
    tK = t + 273.15;
  elseif units == 'K'
    tK = t;
  else
    fprintf('error: unknown units %c, returning absolute zero\n', units);
    tK = 0;
  end

  % convert Kelvin to output temps
  tC = tK - 273.15;
  tF = 9/5*tC + 32;
  
end
</code>

====switch statement====

The above problem is actually better done with a switch statement. Switch statements perform conditional execution based on the value of a variable or an expression. The general form is
<code matlab>
switch expression
  case value1
    action1
  case value2
    action2
  case value3
    action3
  otherwise
    action4
end
</code>

Here's a solution to the problem using a ''switch'' statement.
<code matlab>
function [tK, tC, tF] = temp2kcf(t, units);
% convert temperature t in units 'C', 'F', or 'K' to all three of those units

  % convert input temp to Kelvin
  switch units
    case 'F'
      tK = 5/9*(t-32) + 273.15;      
    case 'C'
      tK = t + 273.15;
    case 'K'
      tK = t;  
    otherwise
      fprintf('error: unknown units %c, returning absolute zero\n', units);
      tK = 0;
  end
  
  % convert Kelvin to output temps
  tC = tK - 273.15;
  tF = 9/5*tC + 32;
  
end
</code>
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