MATLAB Language Conditions IF-ELSEIF condition


Example

Using else we can perform some task when the condition is not satisfied. But what if we want to check a second condition in case that the first one was false. We can do it this way:

a = 9;
if mod(a,2)==0   % MOD - modulo operation, return the remainder after division of 'a' by 2
    disp('a is even')
else
    if mod(a,3)==0
        disp('3 is a divisor of a')
    end
end

OUTPUT:
3 is a divisor of a

This is also called "nested condition", but here we have a speciel case that can improve code readability, and reduce the chance for anr error - we can write:

a = 9;
if mod(a,2)==0
    disp('a is even')
elseif mod(a,3)==0
    disp('3 is a divisor of a')
end

OUTPUT:
3 is a divisor of a

using the elseif we are able to check another expression within the same block of condition, and this is not limited to one try:

a = 25;
if mod(a,2)==0
    disp('a is even')
elseif mod(a,3)==0
    disp('3 is a divisor of a')
elseif mod(a,5)==0
    disp('5 is a divisor of a')
end

OUTPUT:
5 is a divisor of a

Extra care should be taken when choosing to use elseif in a row, since only one of them will be executed from all the if to end block. So, in our example if we want to display all the divisors of a (from those we explicitly check) the example above won't be good:

a = 15;
if mod(a,2)==0
    disp('a is even')
elseif mod(a,3)==0
    disp('3 is a divisor of a')
elseif mod(a,5)==0
    disp('5 is a divisor of a')
end

OUTPUT:
3 is a divisor of a

not only 3, but also 5 is a divisor of 15, but the part that check the division by 5 is not reached if any of the expressions above it was true.

Finally, we can add one else (and only one) after all the elseif conditions to execute a code when none of the conditions above are met:

a = 11;
if mod(a,2)==0
    disp('a is even')
elseif mod(a,3)==0
    disp('3 is a divisor of a')
elseif mod(a,5)==0
    disp('5 is a divisor of a')
else
    disp('2, 3 and 5 are not divisors of a')
end

OUTPUT:
2, 3 and 5 are not divisors of a