MATLAB: Am I getting invalid expression

homeworkMATLAB

clear; clc
h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
counter = 0 ;
for lambda = 800:6:854
    counter = counter + 1 ;
    Lambda(counter) = lambda ;
    E(counter) = ((h * c) / lambda) / J2eV ;
    if ((E > 0.673 && (E < 0.678))
       disp('Energy in eV')
    end
end
E 
Lambda

Best Answer

You should declare Lambda and E as you made for counter.
You also had some flaws in the if condition (a missing parenthesis, and declare the indexes to E)
I made a quick review on the code, and I did not check whether it is optimized or not.
It follows below. =)
Cheers
clear; clc
h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
counter = 0 ;
Lambda = zeros; % declare as zeros

E = zeros;      % declare as zeros
for lambda = 800:6:854
    counter = counter + 1 ;
    Lambda(counter) = lambda ;
    E(counter) = ((h * c) / lambda) / J2eV ;
    if ((E(counter) > 0.673) && (E(counter) < 0.678)) % missing parenthesis and insert indexes to E
       disp('Energy in eV')
    end
end
E 
Lambda
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