second expression and second statement doesn't excuted in else if ?

why the second condition and second statments don't take into account (doeasn't excuted ) ? when I excuted the code only the first condition and its statment excuted as well as to the last statement

if condition 1
    do some calculation 1
elseif condition 2
    do some calculation 2
else
    do some calculation 3
end

[Torsten]

The most probable answer is: condition 2 was never true.

To tell you something more useful, we have to see your code.

[omar th]

first thank you for your fast response,,, regarding to my question actually my code is very long and complicated that's why I didn't share it. So, when I run my code the second condition show me second condition is true and show me messege with that BUT the statement doesn't excuted. It's excuted only when I removed the first condition and make it in the following way.

if condition 2
    do some calculation 2
else
    do some calculation 3
end  

[Voss]

It could be that the second conditon was never true when the first condition was false.

if true % 1st condition always true
    
elseif true % 2nd condition also always true but never checked
    
else
    
end

Answer 1

[Steven Lord]

In an if / elseif / else statement like this:

%{
if condition 1
    do some calculation 1
elseif condition 2
    do some calculation 2
else
    do some calculation 3
end
%}

one and only one of calculations 1, 2, and 3 will be executed each time this section of code runs. I've wrapped it in a block comment so I can run code later in this answer without having the code above error because MATLAB can't run "if condition 1".

If condition 1 is true, MATLAB will execute calculation 1 and then will skip to immediately after the end. MATLAB doesn't even check condition 2 in this case. So condition 2 could error if it were executed and MATLAB wouldn't care.

if true
    disp('Hello')
elseif ones(2) > ones(3) % mismatched sizes, this check would error
    disp('Goodbye')
end

Hello

If condition 1 is false and condition 2 is true, MATLAB will execute calculation 2 and then will skip to immediately after the end.

if false
    disp('Hello')
elseif true
    disp('Goodbye')
else
    disp('What?')
end

Goodbye

If condition 1 is false and condition 2 is false, MATLAB will execute calculation 3 and then will skip to immediately after the end.

if false
    disp('Hello')
elseif false
    disp('Goodbye')
else
    disp('What?')
end

What?

Another potential problem you could be experiencing is that your conditions involved vectors and you expected the body of the if statement to operate only on those elements of the vector that satisfied the condition, then for MATLAB to check the rest of the elements against the condition of the elseif statement, etc.

x = 1:5;
if x > 3 % [false false false true true]
    disp('Hello')
elseif x > 1 % [false true true true true]
    disp('Goodbye')
else
    disp('What?')
end

What?

that is not how MATLAB behaves. If the condition of an if or elseif statement is neither a scalar nor an empty, all the elements of the condition must be true for the condition to be satisfied. If there's even one false (as in the x > 1 case in the example above) the body of that if or elseif is not executed. For this case you'd want to use logical indexing. And you'd probably want to be careful about the order in which you executed those steps.

y = zeros(size(x));
y(x > 3) = x(x > 3).^2

y = 1×5

0 0 0 16 25

y(x > 1) = x(x > 1).^3

y = 1×5

0 8 27 64 125

z = zeros(size(x));
z(x > 1) = x(x > 1).^3

z = 1×5

0 8 27 64 125

z(x > 3) = x(x > 3).^2

z = 1×5

0 8 27 16 25

[omar th]

Great Answer, I really appreciate that, its worked, I re-arranged the priority of conditions according to what I want in the code, thanks again