If-elseif-else statements in MATLAB

Introduction

If-elseif-else statements help your program make choices. They run different code depending on conditions.

Deciding what message to show based on a user's score.

Choosing different actions depending on sensor readings.

Running special code only if a number is positive, negative, or zero.

Checking multiple conditions one after another to find the right match.

Syntax

MATLAB

if condition1
    % code to run if condition1 is true
elseif condition2
    % code to run if condition2 is true
else
    % code to run if none of the above conditions are true
end

Each condition is a logical test that results in true or false.

The elseif and else parts are optional but help check multiple cases.

Examples

Runs code only if x is greater than zero.

MATLAB

if x > 0
    disp('Positive number')
end

Checks if x is positive, zero, or negative and shows a message.

MATLAB

if x > 0
    disp('Positive')
elseif x == 0
    disp('Zero')
else
    disp('Negative')
end

Shows weather description based on temperature ranges.

MATLAB

if temperature > 30
    disp('Hot')
elseif temperature > 20
    disp('Warm')
else
    disp('Cold')
end

Sample Program

This program checks the temperature and prints if it is hot, warm, or cold.

MATLAB

temperature = 25;

if temperature > 30
    disp('It is hot outside.')
elseif temperature > 20
    disp('It is warm outside.')
else
    disp('It is cold outside.')
end

Important Notes

Always end your if-elseif-else block with end in MATLAB.

Conditions are checked in order. Once one is true, the rest are skipped.

You can have many elseif parts to check multiple conditions.

Summary

If-elseif-else lets your program choose between different actions.

Conditions are tested in order until one is true.

Use end to close the whole if block.

Practice

1. What does an if-elseif-else statement do in MATLAB?

easy

A. It creates a variable.

B. It repeats a block of code multiple times.

C. It defines a function.

D. It chooses one action based on conditions.

Solution

1. Step 1: Understand the purpose of if-elseif-else

   The if-elseif-else structure lets the program check conditions one by one and run the code for the first true condition.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data, so these are not correct.

3. Final Answer:

   It chooses one action based on conditions. -> Option D

4. Quick Check:

   If-elseif-else = choose action [OK]

Hint: If you see conditions, think if-elseif-else [OK]

Common Mistakes:

• Confusing if-elseif-else with loops
• Thinking it defines functions
• Believing it creates variables

2. Which of the following is the correct syntax to start an if-elseif-else block in MATLAB?

easy

A. if x > 0
elseif x == 0
else
end

B. if x > 0 elseif x == 0 else end

C. if (x > 0) then elseif (x == 0) else end

D. if x > 0; elseif x == 0; else; end

Solution

1. Step 1: Check MATLAB syntax rules

   MATLAB requires each keyword (if, elseif, else, end) on its own line or separated by line breaks, without 'then'.

2. Step 2: Analyze each option

   if x > 0 elseif x == 0 else end uses line breaks correctly. if x > 0 elseif x == 0 else end misses line breaks. if (x > 0) then elseif (x == 0) else end uses 'then' which is invalid. if x > 0; elseif x == 0; else; end uses semicolons incorrectly in control flow.

3. Final Answer:

   if x > 0 elseif x == 0 else end -> Option A

4. Quick Check:

   MATLAB if-elseif-else needs line breaks [OK]

Hint: Use line breaks, no 'then' in MATLAB if statements [OK]

Common Mistakes:

• Using 'then' keyword
• Putting all keywords on one line without breaks
• Using semicolons after if/elseif/else

3. What will be the output of this MATLAB code?

score = 75;
if score >= 90
    grade = 'A';
elseif score >= 80
    grade = 'B';
elseif score >= 70
    grade = 'C';
else
    grade = 'F';
end
disp(grade)

medium

A. C

B. B

C. A

D. F

Solution

1. Step 1: Check conditions in order

   score is 75, first condition score >= 90 is false, second score >= 80 is false, third score >= 70 is true.

2. Step 2: Assign grade and display

   Since third condition is true, grade = 'C' is assigned and displayed.

3. Final Answer:

   C -> Option A

4. Quick Check:

   75 >= 70 -> grade C [OK]

Hint: Check conditions top to bottom, first true wins [OK]

Common Mistakes:

• Choosing grade B or A incorrectly
• Ignoring order of conditions
• Forgetting to use end to close if block

4. Identify the error in this MATLAB code snippet:

value = 10;
if value > 5
    disp('Greater than 5')
elseif value < 5
    disp('Less than 5')
else
    disp('Equal to 5')

medium

A. Missing semicolon after disp statements

B. Missing end to close the if block

C. Incorrect use of elseif instead of else if

D. Using single quotes instead of double quotes

Solution

1. Step 1: Check if block completeness

   The if-elseif-else block must end with an end keyword in MATLAB to close it properly.

2. Step 2: Verify other syntax elements

   Semicolons after disp are optional, elseif is correct keyword, and single quotes are correct for strings in MATLAB.

3. Final Answer:

   Missing end to close the if block -> Option B

4. Quick Check:

   if blocks need end [OK]

Hint: Always close if with end [OK]

Common Mistakes:

• Forgetting end keyword
• Confusing elseif with else if
• Thinking semicolons are mandatory after disp

5. You want to write a MATLAB function that returns:
- 'Positive' if input > 0
- 'Zero' if input == 0
- 'Negative' if input < 0
Which if-elseif-else structure correctly implements this?

hard

A. if x > 0
result = 'Positive';
else if x == 0
result = 'Zero';
else
result = 'Negative';
end

B. if x >= 0
result = 'Positive';
elseif x == 0
result = 'Zero';
else
result = 'Negative';
end

C. if x > 0
result = 'Positive';
elseif x == 0
result = 'Zero';
else
result = 'Negative';
end

D. if x > 0
result = 'Positive';
elseif x > 0
result = 'Zero';
else
result = 'Negative';
end

Solution

1. Step 1: Check condition order and correctness

   if x > 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end correctly checks x > 0 first, then x == 0, else negative. This covers all cases without overlap.

2. Step 2: Analyze other options for errors

   if x >= 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end wrongly treats x == 0 as Positive. if x > 0 result = 'Positive'; else if x == 0 result = 'Zero'; else result = 'Negative'; end uses invalid 'else if' instead of 'elseif'. if x > 0 result = 'Positive'; elseif x > 0 result = 'Zero'; else result = 'Negative'; end repeats x > 0 condition twice, missing zero case.

3. Final Answer:

   if x > 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end -> Option C

4. Quick Check:

   Check conditions in order, use elseif [OK]

Hint: Use elseif, not else if; order conditions carefully [OK]

Common Mistakes:

• Using else if instead of elseif
• Overlapping conditions
• Wrong order causing incorrect results