Colon operator for ranges in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple colon operator range

What is the output of this MATLAB code?

a = 3:7;

MATLAB

a = 3:7;

A [7 6 5 4 3]

B [3 5 7]

C [3 4 5 6 7]

D [3 4 5 6]

💡 Hint

The colon operator creates a vector starting at the first number and ending at the second, increasing by 1 by default.

The colon operator a:b creates a row vector starting at a, ending at b, with step size 1. So 3:7 is [3 4 5 6 7].

❓ Predict Output

intermediate

Output with custom step size in colon operator

What is the output of this MATLAB code?

b = 1:2:9;

MATLAB

b = 1:2:9;

A [1 4 7]

B [1 3 5 7 9]

C [1 2 3 4 5 6 7 8 9]

D [2 4 6 8]

💡 Hint

The colon operator with three parts is start:step:end.

1:2:9 means start at 1, add 2 each time, stop before exceeding 9. So the vector is [1 3 5 7 9].

❓ Predict Output

advanced

Output when step size does not evenly fit range

What is the output of this MATLAB code?

c = 0:0.3:1;

MATLAB

c = 0:0.3:1;

A [0 0.3 0.6 0.9 1.2]

B [0 0.3 0.6]

C [0 0.3 0.6 0.9 1.0]

D [0 0.3 0.6 0.9]

💡 Hint

The colon operator stops before exceeding the end value.

Starting at 0, adding 0.3 each time: 0, 0.3, 0.6, 0.9, next would be 1.2 which is >1, so stop at 0.9.

❓ Predict Output

advanced

Output of colon operator with negative step

What is the output of this MATLAB code?

d = 5:-1:1;

MATLAB

d = 5:-1:1;

A [5 4 3 2 1]

B [1 2 3 4 5]

C [5 4 3 2]

D [5 6 7 8 9]

💡 Hint

The colon operator can count down if the step is negative.

5:-1:1 counts down from 5 to 1 by subtracting 1 each step, so the vector is [5 4 3 2 1].

🧠 Conceptual

expert

Number of elements in colon operator range

How many elements are in the vector created by this MATLAB code?

e = 2:0.5:5;

MATLAB

e = 2:0.5:5;

A 7

B 6

C 9

D 8

💡 Hint

Count elements starting at 2, adding 0.5 until you reach or pass 5.

Elements are 2, 2.5, 3, 3.5, 4, 4.5, 5.0. That's 7 elements, so answer is 7.

Practice

1. What does the MATLAB expression 1:5 produce?

easy

A. [1 3 5]

B. [5 4 3 2 1]

C. [1 2 3 4 5]

D. [1 2 3 4]

Solution

1. Step 1: Understand the colon operator syntax

   The expression start:end creates a sequence from start to end with step 1 by default.

2. Step 2: Apply to given expression

   Here, 1:5 means numbers from 1 to 5 increasing by 1: 1, 2, 3, 4, 5.

3. Final Answer:

   [1 2 3 4 5] -> Option C

4. Quick Check:

   1 to 5 by 1 = [1 2 3 4 5] [OK]

Hint: Colon with two numbers counts up by 1 [OK]

Common Mistakes:

• Thinking it skips numbers
• Confusing start and end order
• Assuming it counts down automatically

2. Which of the following is the correct syntax to create a vector from 10 down to 2 with step -2 in MATLAB?

easy

A. 10:-2:2

B. 10:2:-2

C. 10--2:2

D. 10:-2:-2

Solution

1. Step 1: Recall colon operator with step syntax

   The syntax is start:step:end. For counting down, step must be negative.

2. Step 2: Check each option

   10:-2:2 uses 10:-2:2, which counts down from 10 to 2 by -2 correctly.

3. Final Answer:

   10:-2:2 -> Option A

4. Quick Check:

   Descending with negative step = 10:-2:2 [OK]

Hint: Use negative step for descending ranges [OK]

Common Mistakes:

• Putting step after end value
• Using positive step for descending
• Syntax errors with double minus signs

3. What is the output of the MATLAB code:

vec = 3:3:12;

disp(vec);

medium

A. [3 4 5 6 7 8 9 10 11 12]

B. [3 6 9 12]

C. [3 6 9]

D. [12 9 6 3]

Solution

1. Step 1: Understand the colon operator with step

   The syntax start:step:end creates numbers from start to end increasing by step.

2. Step 2: Calculate the sequence

   Starting at 3, add 3 each time: 3, 6, 9, 12. Since 12 is included, the sequence ends there.

3. Final Answer:

   [3 6 9 12] -> Option B

4. Quick Check:

   3 to 12 by 3 = [3 6 9 12] [OK]

Hint: Multiply step by count until reaching or passing end [OK]

Common Mistakes:

• Stopping before including end if exact
• Confusing step with end value
• Assuming step is always 1

4. Identify the error in this MATLAB code:

range = 5:0.5:3;

medium

A. Empty vector because start > end with positive step

B. Syntax error due to decimal step

C. Vector counts down correctly

D. Step must be integer

Solution

1. Step 1: Analyze start, step, and end values

   Start is 5, end is 3, step is 0.5 (positive).

2. Step 2: Understand colon operator behavior

   With positive step, MATLAB counts up. Since 5 > 3, no values satisfy the condition, so the vector is empty.

3. Final Answer:

   Empty vector because start > end with positive step -> Option A

4. Quick Check:

   Positive step but start > end = empty vector [OK]

Hint: Step sign must match direction from start to end [OK]

Common Mistakes:

• Assuming decimal steps cause syntax errors
• Expecting vector to count down with positive step
• Thinking step must be integer

5. You want to create a vector in MATLAB that starts at 0, goes up to 1, but only includes values less than 1 with step 0.2. Which expression correctly does this?

hard

A. 0:0.2:1

B. 0:0.2:<1

C. 0:0.2:1.1

D. 0:0.2:0.9

Solution

1. Step 1: Understand the requirement

   The vector should start at 0, increase by 0.2, and include values less than 1 (not including 1).

2. Step 2: Check which end value excludes 1

   Using 0:0.2:1 includes 1 since it matches the sequence (0, 0.2, 0.4, 0.6, 0.8, 1). Since 1 is included, it violates the condition.

3. Step 3: Choose end value less than 1

   Using 0:0.2:0.9 stops at 0.8 (0.8 + 0.2 = 1.0 > 0.9), which is less than 1, so it meets the condition.

4. Final Answer:

   0:0.2:0.9 -> Option D

5. Quick Check:

   End less than 1 excludes 1 from vector [OK]

Hint: Set end value just below the limit to exclude it [OK]

Common Mistakes:

• Using end value equal to limit includes it
• Trying invalid syntax like <1
• Assuming floating point precision excludes end automatically