Relational expressions in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained relational expressions

What is the output of this MATLAB code snippet?

MATLAB

a = 5;
b = 10;
c = 15;
result = (a < b) & (b < c);
disp(result);

A [1 1]

B 0

C Error: Undefined function or variable 'result'

D 1

💡 Hint

Recall that relational expressions return logical 1 (true) or 0 (false).

Both conditions (a < b) and (b < c) are true, so the logical AND (&) returns 1.

❓ Predict Output

intermediate

Relational expression with arrays

What is the output of this MATLAB code?

MATLAB

x = [2, 4, 6];
y = [3, 4, 5];
result = x >= y;
disp(result);

A [0 1 1]

B [1 1 1]

C [0 0 0]

D Error: Matrix dimensions must agree.

💡 Hint

Relational operators compare elements element-wise in arrays of the same size.

Comparing element-wise: 2>=3 is false (0), 4>=4 is true (1), 6>=5 is true (1).

❓ Predict Output

advanced

Result of mixing relational and logical operators

What does this MATLAB code display?

MATLAB

a = 7;
b = 5;
c = 7;
result = (a == c) | (b > a);
disp(result);

A [1 0]

B 0

C 1

D Error: Undefined function or variable 'result'

💡 Hint

The OR operator (|) returns true if either condition is true.

a == c is true (7 == 7), b > a is false (5 > 7). True OR false is true (1).

❓ Predict Output

advanced

Relational expression with mixed data types

What is the output of this MATLAB code?

MATLAB

x = 3;
y = '3';
result = (x == y);
disp(result);

A 0

B 1

C Error: Conversion to double from char is not possible.

D Error: Undefined function or variable 'result'

💡 Hint

MATLAB compares numeric and char types differently in relational expressions.

Numeric 3 is not equal to char '3', so the result is 0 (false).

❓ Predict Output

expert

Logical indexing with relational expressions

What is the output of this MATLAB code?

MATLAB

A = [10, 20, 30, 40, 50];
idx = A > 25;
result = A(idx);
disp(result);

A [25 30 40 50]

B [30 40 50]

C [10 20 25]

D Error: Index exceeds matrix dimensions.

💡 Hint

Logical indexing selects elements where the condition is true.

Elements greater than 25 are 30, 40, and 50, so result is [30 40 50].

Practice

1. Which of the following relational operators in MATLAB checks if two values are NOT equal?

easy

A. ==

B. <=

C. >=

D. ~=

Solution

1. Step 1: Understand the meaning of relational operators

   The operator == checks equality, ~= checks inequality, and >=, <= check greater or equal and less or equal respectively.

2. Step 2: Identify the operator for NOT equal

   The operator ~= means NOT equal in MATLAB.

3. Final Answer:

   ~= -> Option D

4. Quick Check:

   NOT equal operator = ~= [OK]

Hint: Remember: ~= means NOT equal in MATLAB [OK]

Common Mistakes:

• Confusing == with ~=
• Using = instead of ==
• Mixing up >= and >

2. Which of the following is the correct syntax to check if variable a is greater than or equal to 10 in MATLAB?

easy

A. a >== 10

B. a >= 10

C. a =< 10

D. a => 10

Solution

1. Step 1: Recall MATLAB relational operator syntax

   MATLAB uses >= to mean greater than or equal to.

2. Step 2: Check each option for correct syntax

   a >= 10 uses >= correctly. Options A, B, and C use invalid or reversed operators.

3. Final Answer:

   a >= 10 -> Option B

4. Quick Check:

   Greater or equal operator = >= [OK]

Hint: Use >= for greater or equal, not => or =< [OK]

Common Mistakes:

• Writing => instead of >=
• Writing =< instead of <=
• Adding extra = signs

3. What is the output of the following MATLAB code?

a = 5; b = 7;
result = (a < b) & (b <= 7);
disp(result);

medium

A. 1

B. 0

C. Error

D. [1 0]

Solution

1. Step 1: Evaluate each relational expression

   a < b is 5 < 7 which is true (1). b <= 7 is 7 <= 7 which is true (1).

2. Step 2: Apply logical AND operator &

   Both expressions are true, so (1 & 1) equals 1 (true).

3. Final Answer:

   1 -> Option A

4. Quick Check:

   True & True = 1 [OK]

Hint: True & True gives 1, false & anything gives 0 [OK]

Common Mistakes:

• Confusing & with &&
• Expecting output as logical word instead of 1
• Misreading <= operator

4. Identify the error in this MATLAB code snippet:

x = 10;
if x = 10
    disp('Equal to 10');
end

medium

A. Using = instead of == in if condition

B. Missing semicolon after disp statement

C. Incorrect use of end keyword

D. Variable x is not initialized

Solution

1. Step 1: Check the if condition syntax

   In MATLAB, = is assignment, == is comparison. Using = in if causes error.

2. Step 2: Confirm other parts are correct

   Semicolon after disp is optional, end is correctly used, x is initialized.

3. Final Answer:

   Using = instead of == in if condition -> Option A

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use == for comparison inside if, not = [OK]

Common Mistakes:

• Using = instead of ==
• Thinking semicolon is mandatory after disp
• Misplacing end keyword

5. Given a vector v = [3, 6, 9, 12], which MATLAB expression returns a logical array indicating elements greater than 5 and less than or equal to 10?

hard

A. v > (5 & v) <= 10

B. v > 5 && v <= 10

C. (v > 5) & (v <= 10)

D. (v > 5) | (v <= 10)

Solution

1. Step 1: Understand vector relational operations

   Relational operators applied to vectors return logical arrays element-wise.

2. Step 2: Combine conditions correctly with parentheses and &

   Use parentheses around each condition: (v > 5) & (v <= 10) to get elements satisfying both.

3. Step 3: Check other options for syntax errors

   v > 5 && v <= 10 uses short-circuit &&, invalid for vectors. v > (5 & v) <= 10 is invalid syntax. (v > 5) | (v <= 10) uses OR instead of AND.

4. Final Answer:

   (v > 5) & (v <= 10) -> Option C

5. Quick Check:

   Use parentheses with & for combined conditions [OK]

Hint: Always use parentheses around each relational condition [OK]

Common Mistakes:

• Using && instead of & for array operations
• Using | instead of & for AND
• Writing invalid combined expressions