Problem with Matlab Repeating menu with a loop, with user determining when it stops

I have to make a repeating code that allows the user to select one of four options. One calculates the area of either a rectangle or triangle that they enter the specs for, one calculates the perimeter, another exits the program, and the first option allows them to enter the specs for the shape.

I want this menu to repeat infinitely until user decides its time to exit:

Geometric Calculator. Please select an option below:
Press 1 to enter values and shape code (r/R for Rectangle and t/T for Triangle).
Press 2 to calculate the area of said shape.
Press 3 to calculate the perimeter of said shape.
Press 4 to exit program.

selection=input('Enter a selection>> ');

------my main script-----

menu();
global selection;
global sideone;
global sidetwo;
global shapecode;

if selection==1 || selection==2 || selection==3 || selection==4
    if selection ==1
        sideone=input('Please enter a value for the first side>> ');
        sidetwo=input('Please enter a value for the secon side>> ');
        shapecode=input('Please enter the shape code (r/R for Rectangle and t/T for triangle)>> ');
        menu();
    elseif selection==2
        calcArea();
        menu();
    elseif selection==3
        calcPerim();
        menu();
    else
        disp('Thank you for using the geometric calculator');
    end
else
    disp('Please enter a valid menu option (1 through 4)');
end

----menu----

function [] = menu()
disp({'Press 1 to enter values and shape code (r/R for Rectangle and t/T for Triangle).',
'Press 2 to calculate the area of said shape.',
'Press 3 to calculate the perimeter of said shape.',
'Press 4 to exit program.'})
global selection;
selection=input('Enter a selection>> ');
end

----calcArea----

function [] = calcArea()
global sideone;
global sidetwo;
global shapecode;
area=0;
if shapecode=='R' || shapecode=='r'
    area=sideone*sidetwo;
    fprintf('The area is %0.3f \n',area);
elseif shapecode=='T' || shapecode=='t'
    area=.5*sideone*sidetwo;
    fprintf('the area is %0.3f \n',area);
end

----calcPerim----

function [] = calcPerim()
global sideone;
global sidetwo;
global shapecode;
perim=0;
if shapecode=='R' || shapecode=='r'
    perim=sideone+sideone+sidetwo+sidetwo;
    fprintf('The perimeter is %0.3f \n',perim);
elseif shapecode=='T' || shapecode=='t'
    perim=sideone+sidetwo+sqrt((sideone^2)+(sidetwo^2));
    fprintf('the perimeter is %0.3f \n',perim);
end

The error i get:

>> quiz7wk10
    'Press 1 to enter values and shape code (r/R for Rectangle and t/T for Triangle).'
    'Press 2 to calculate the area of said shape.'
    'Press 3 to calculate the perimeter of said shape.'
    'Press 4 to exit program.'

Enter a selection>> 2
Operands to the || and && operators must be convertible to logical scalar values.

Error in quiz7wk10 (line 7)
if selection==1 || selection==2 || selection==3 || selection==4