String formatting (sprintf) in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of sprintf with integer and float formatting

What is the output of the following MATLAB code?

str = sprintf('Value: %d, Pi approx: %.2f', 7, 3.14159); disp(str);

MATLAB

str = sprintf('Value: %d, Pi approx: %.2f', 7, 3.14159); disp(str);

A Value: 7, Pi approx: 3.14159

B Value: 7, Pi approx: 3.14

C Value: 7, Pi approx: 3.1

D Value: 7, Pi approx: 3

💡 Hint

Look at the %.2f format specifier; it rounds to two decimal places.

The %d formats the integer 7 as is. The %.2f rounds the float 3.14159 to two decimal places, resulting in 3.14.

❓ Predict Output

intermediate

Using sprintf to format a date string

What will be the output of this MATLAB code?

day = 5; month = 9; year = 2024; str = sprintf('Date: %02d/%02d/%04d', day, month, year); disp(str);

MATLAB

day = 5; month = 9; year = 2024; str = sprintf('Date: %02d/%02d/%04d', day, month, year); disp(str);

A Date: 5/9/2024

B Date: 05/9/2024

C Date: 05/09/2024

D Date: 5/09/2024

💡 Hint

The %02d means pad with zeros to 2 digits, %04d pads to 4 digits.

The day and month are padded with zeros to two digits, so 5 becomes 05 and 9 becomes 09. The year is padded to 4 digits, but it is already 4 digits.

❓ Predict Output

advanced

Output of sprintf with mixed format specifiers

What is the output of this MATLAB code?

str = sprintf('Hex: %X, Oct: %o, Char: %c', 255, 8, 65); disp(str);

MATLAB

str = sprintf('Hex: %X, Oct: %o, Char: %c', 255, 8, 65); disp(str);

A Hex: FF, Oct: 10, Char: A

B Hex: ff, Oct: 8, Char: 65

C Hex: FF, Oct: 8, Char: A

D Hex: 255, Oct: 10, Char: 65

💡 Hint

Remember %X prints uppercase hex, %o prints octal, %c prints character from ASCII code.

255 in hex is FF, 8 in octal is 10, and ASCII code 65 is character 'A'.

❓ Predict Output

advanced

sprintf with width and left alignment

What will this MATLAB code display?

str = sprintf('|%-10s|%5d|', 'Hi', 42); disp(str);

MATLAB

str = sprintf('|%-10s|%5d|', 'Hi', 42); disp(str);

A |Hi | 42|

B | Hi| 42|

C |Hi |42 |

D |Hi| 42|

💡 Hint

%-10s means left-align string in 10 spaces; %5d means right-align integer in 5 spaces.

The string 'Hi' is left aligned in a 10-character field, padded with spaces on the right. The number 42 is right aligned in a 5-character field, padded with spaces on the left.

🧠 Conceptual

expert

Understanding sprintf behavior with multiple format specifiers

Consider this MATLAB code:

str = sprintf('%d %d %d', 1, 2); disp(str);

What happens when you run this code?

A It prints '1 2' ignoring the last format specifier.

B It prints '1 2 0' because missing arguments default to zero.

C It prints '1 2 2' repeating the last argument.

D It raises an error because there are fewer input arguments than format specifiers.

💡 Hint

Check how MATLAB handles missing arguments for sprintf.

MATLAB requires the number of arguments to match the number of format specifiers. Missing arguments cause an error.

Practice

1. What does the sprintf function in MATLAB do?

easy

A. Creates a formatted string by inserting values into a template

B. Reads input from the user

C. Plots data on a graph

D. Saves variables to a file

Solution

1. Step 1: Understand the purpose of sprintf

   sprintf is used to create text with values inserted in a specific format.

2. Step 2: Compare options to function behavior

   Only Creates a formatted string by inserting values into a template describes creating formatted strings, which matches sprintf's role.

3. Final Answer:

   Creates a formatted string by inserting values into a template -> Option A

4. Quick Check:

   sprintf formats strings = A [OK]

Hint: Remember: sprintf formats text, not input or files [OK]

Common Mistakes:

• Confusing sprintf with input functions
• Thinking sprintf plots graphs
• Assuming sprintf saves files

2. Which of the following is the correct syntax to format an integer variable num using sprintf in MATLAB?

easy

A. str = sprintf('%s', num);

B. str = sprintf('%c', num);

C. str = sprintf('%d', num);

D. str = sprintf('%f', num);

Solution

1. Step 1: Identify format specifier for integers

   The format specifier %d is used for integers in sprintf.

2. Step 2: Match specifier with variable type

   Since num is an integer, %d is correct; others are for strings, floats, or characters.

3. Final Answer:

   str = sprintf('%d', num); -> Option C

4. Quick Check:

   Integer format = %d = D [OK]

Hint: Use %d for integers, %s for strings, %f for floats [OK]

Common Mistakes:

• Using %s for numbers
• Using %f for integers
• Using %c for non-character data

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

str = sprintf('Value: %0.2f', 3.14159); disp(str);

medium

A. Value: 3.1

B. Value: 3.14

C. Value: 3.14159

D. Value: 03.14

Solution

1. Step 1: Understand the format specifier %0.2f

   This means a floating-point number with 2 digits after the decimal point, padded with zeros if needed.

2. Step 2: Apply formatting to 3.14159

   Rounded to 2 decimals, 3.14159 becomes 3.14, no extra zero padding before the number.

3. Final Answer:

   Value: 3.14 -> Option B

4. Quick Check:

   %.2f rounds float to 2 decimals = Value: 3.14 [OK]

Hint: %.2f rounds float to 2 decimals in sprintf [OK]

Common Mistakes:

• Expecting full decimal without rounding
• Confusing zero padding before decimal
• Ignoring rounding rules

4. Identify the error in this MATLAB code:

str = sprintf('Name: %s, Age: %d', 25, 'John');

medium

A. sprintf cannot format multiple variables

B. Missing semicolon at the end

C. Incorrect format specifier for string

D. The order of variables does not match format specifiers

Solution

1. Step 1: Check format specifiers and variable order

   The format expects a string first (%s) then an integer (%d), but variables are 25 (int) then 'John' (string).

2. Step 2: Identify mismatch cause

   Variables are swapped, causing wrong data types for specifiers.

3. Final Answer:

   The order of variables does not match format specifiers -> Option D

4. Quick Check:

   Variable order must match specifiers = A [OK]

Hint: Match variable order exactly to format specifiers [OK]

Common Mistakes:

• Swapping variable order
• Ignoring type mismatch
• Assuming sprintf auto-corrects order

5. You want to create a formatted string showing a product name and price with 2 decimals, like "Product: Laptop, Price: $999.99". Which sprintf call correctly formats name = 'Laptop' and price = 999.987?

hard

A. sprintf('Product: %s, Price: $%0.2f', name, price)

B. sprintf('Product: %s, Price: $%d', price, name)

C. sprintf('Product: %s, Price: $%f', name, price)

D. sprintf('Product: %s, Price: $%.2d', name, price)

Solution

1. Step 1: Identify correct format specifiers

   %s for string name, %0.2f for float price with 2 decimals.

2. Step 2: Check variable order and formatting

   sprintf('Product: %s, Price: $%0.2f', name, price) uses correct order and formats price to 2 decimals, rounding 999.987 to 999.99.

3. Final Answer:

   sprintf('Product: %s, Price: $%0.2f', name, price) -> Option A

4. Quick Check:

   String + float with 2 decimals = B [OK]

Hint: Use %s for strings and %0.2f for 2-decimal floats [OK]

Common Mistakes:

• Swapping variable order
• Using %d for floats
• Using incorrect precision specifier