How do I Take in input string and insert that string into an if statment

I want to take a user input of two options that are strings, either SI or imperial units, and insert this into an if statement in order to execute one script if SI, and go to another else statement if imperial units.

Here's my code condensed:

 H = input('Enter the word SI or imperial for Temp., pressure and density units','s')

 if input == 'SI'

H = input('Enter Altitude in km: '); if (H <= 11)&&(H > 0) kt = -6.5; Tb = 288.15; Hb = 0; T = kt*(H-Hb)+Tb; %%Temp Pb = rho_o*R*Tb; %% base pressure P = Pb*((1+(kt/Tb)*(H-Hb))^-((g)/(R*kt))); %% Pressure c = sqrt(R*T*G); %% Speed of sound rho = P/(R*T); %% Density

         delta = P/Pb; %%pressure ratio
         theta = (Tb/To)*(1+(kt/Tb)*(H-Hb));           %%Temp ratio
         sigma = delta/theta;  %%density ratio

         fprintf('delta = %f\n theta = %f\n sigma = %f\n P = %f Pa\n T = %f K\n rho = %f kg/m^3',delta, theta, sigma, P, T, rho) %%output pressure, temp.,density & ratios for all three also

……………

else %some other code for imperial units or conversion that isn't written yet

[Stephen23]

Do NOT use input as a variable name! Then you shadow the input command.

Answer 1

[Bob Thompson]

I usually make this kind of check with a string comparison as the if condition.

if strcmp(input,'SI')==1;
 ...
else
 ...
end

Any time you want to run an if statement on a string though it has to be Exactly what you're looking for. Any extra spaces or characters will return a negative comparison with strcmp. I would suggest telling the user what inputs are expected to help them avoid this.

[Ikenna Okoye]

Ok thanks. I now got this error:

Error using input Not enough input arguments.

Error in Atmosphereto100km (line 4) if strcmp(input,'SI')==1

[Stephen23]

Do NOT use input as a variable name! This shadows the inbuilt input fucntion.

You need to use the name of the variable, not the name of the input function:

H = input('Enter the word SI or imperial for Temp., pressure and density units','s');
if strcmp(H,'SI') % ==1 is not required
    ...
else
    ...
end

Answer 2

[Saifur Rahman Opu]

Write a program main_1.m which will ask the user the input “Select the shape”. The user has the option of typing ‘square’, ‘circle’, ‘rectangle’. Once the user selects the shape, display a message: “The user has selected : shape”. If the user enters any other shape, it should display an error message “Shape is not valid”.

this is my answer

s=input('select the shape')

square='square';

circle='circle';

rectangular='rectangular';

if s==circle

disp('the user has selected:circle')

elseif s==square

disp('the user has selected: square')

elseif s==rectangular

disp('the user has selected:rectangular')

else

disp('invalid shape')

end

but it still error