No-Input: Error Checking Problem

clear, clc
disp('Welcome to Basic Conversion Script');

prompt = 'Please input t for Temperature, l for Length, or m for Mass: ';
z = input (prompt, 's');
w = isempty(z);
if w == 0
    disp('Error! There is not input');
end

while ~(z == 't' || z == 'l' || z == 'm')
    z = input ('Error! Please input wanted values again: ', 's');
    w = isempty(z);
    if w == 0
        disp('Error! There is not input');
    end
    
end

if strcmp(z,'t')
    
    disp('1. To Convert Celsius to Fahrenheit' );
    disp('--');
    disp('2. To Convert Fahrenheit to Celsius ');
    
    x = input('Please choose a number betwenn 1 or 2: ');
    
    w = isempty(x);
    
    if w == 0
        disp('Error! There is not input');
    end
    
    while ~(x == 1 || x == 2)
            
        if strcmp(x, 's')
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        elseif (x < 0) %This if-statement is error checking for any negative values
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        else
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        end
    end
    
    if x == 1
        
        C = input('Enter the Temperatue in Celsius: ');
        w = isempty(C);
        
        if w == 1
            disp('Please Input a number to convert next time');
        end
        
        F = (C * 9/5) + 32;
        
        fprintf('The Temperature in Fahrenheit is: %1.2f\n', F );
        fprintf(1, '\n');
        
    end
    if x==2
        F = input('Enter the Temperatue in Fahrenheit: ');
        w = isempty(F);
        
        if w == 1
            disp('Please Input a number to convert next time');
        end
        
        C = (F - 32) * 5/9;
        
        fprintf('The Temperature in Celcius is: %1.2f\n', C );
        fprintf(1, '\n');
        
    end
    
end

So I'm currently creating a conversion script. And I'm currently trying to do a error check that makes sure it sends out an a error message when the user doesn't input anything.

The error I get is:

Operands to the || and && operators must be convertible to logical scalar values.

Error in Milestone2 (line 11)
while ~(z == 't' || z == 'l' || z == 'm')

Answer 1

[Mehmed Saad]

Replace your while loop conditions

you are comparing z with a single character suppose someone enters

z = 'abdft'

the output of z=='t' will be [0 0 0 0 1] and you dont want that

Use strcmp (check its help)

while ~(strcmp(z,'t')||strcmp(z,'l')||strcmp(z,'m'))

Also you need to reverse this condition

    w = isempty(z);
    if w == 0
    disp('Error! There is not input');
end

because whenever w is empty it will give you 1 while your condition is if w ==0 display error

but error actually comes when w==1

either change

w = ~isempty(z)

or change

if w==1

[Neshant Thiru]

Why can't I get the error checking to work in the:

    while ~(x == 1 || x == 2)
            
        if strcmp(x, 's')
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        elseif (x < 0) %This if-statement is error checking for any negative values
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        else
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        end
    end

[Mehmed Saad]

it is working for me

clear, clc
disp('Welcome to Basic Conversion Script');

prompt = 'Please input t for Temperature, l for Length, or m for Mass: ';
z = input (prompt, 's');
w = ~isempty(z);
if w == 0
    disp('Error! There is not input');
end

while ~(strcmp(z,'t')||strcmp(z,'l')||strcmp(z,'m'))
    z = input ('Error! Please input wanted values again: ', 's');
    w = ~isempty(z);
    if w == 0
        disp('Error! There is not input');
    end
    
end

if strcmp(z,'t')
    
    disp('1. To Convert Celsius to Fahrenheit' );
    disp('--');
    disp('2. To Convert Fahrenheit to Celsius ');
    
    x = input('Please choose a number betwenn 1 or 2: ');
    
    w = ~isempty(x);
    
    if w == 0
        disp('Error! There is not input');
    end
    
    while ~(x == 1 || x == 2)
            
        if strcmp(x, 's')
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        elseif (x < 0) %This if-statement is error checking for any negative values
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        else
            x = input ('Error! Please choose a number betwenn 1 or 2 again: ');
        end
    end
    
    if x == 1
        
        C = input('Enter the Temperatue in Celsius: ');
        w = isempty(C);
        
        if w == 1
            disp('Please Input a number to convert next time');
        end
        
        F = (C * 9/5) + 32;
        
        fprintf('The Temperature in Fahrenheit is: %1.2f\n', F );
        fprintf(1, '\n');
        
    end
    if x==2
        F = input('Enter the Temperatue in Fahrenheit: ');
        w = isempty(F);
        
        if w == 1
            disp('Please Input a number to convert next time');
        end
        
        C = (F - 32) * 5/9;
        
        fprintf('The Temperature in Celcius is: %1.2f\n', C );
        fprintf(1, '\n');
        
    end
    
end

[Mehmed Saad]

the only thing is

 x = input('Please choose a number betwenn 1 or 2: ');

if user put a string an error will occur because input is expecting to get numerical input