String formatting (sprintf) in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sprintf function do in MATLAB?

It creates a formatted string using specified format specifiers and input values, without displaying it on the screen.

beginner

How do you format a floating-point number to show 2 decimal places using sprintf?

Use the format specifier %.2f. For example, sprintf('%.2f', 3.14159) returns '3.14'.

beginner

What is the difference between sprintf and fprintf in MATLAB?

sprintf returns a formatted string without printing it, while fprintf prints the formatted string directly to the command window or a file.

intermediate

How can you include a literal percent sign (%) in a string formatted by sprintf?

Use %% in the format string. For example, sprintf('Progress: 50%% complete') returns 'Progress: 50% complete'.

intermediate

Explain how to format an integer with leading zeros using sprintf.

Use a format specifier like %05d to pad the integer with zeros to a width of 5. For example, sprintf('%05d', 42) returns '00042'.

Which sprintf format specifier would you use to display a number with exactly 3 decimal places?

A %.3f

B %3f

C %.f3

D %f3

The correct format is %.3f, which means a floating-point number with 3 digits after the decimal point.

What does sprintf('Value: %d', 10.5) output in MATLAB?

A Value: %d

B Value: 10.5

C Value: 10

D Error

The %d specifier formats the number as an integer, so 10.5 is converted to 10.

How do you print a string variable name inside a formatted string using sprintf?

A sprintf('Hello %s', name)

B sprintf('Hello %d', name)

C sprintf('Hello %f', name)

D sprintf('Hello %c', name)

Use %s to format strings in sprintf.

What will sprintf('%%d is a placeholder') output?

A %%d is a placeholder

B d is a placeholder

C Error

D %d is a placeholder

Using %% outputs a literal percent sign, so %%d becomes %d in the string.

Which sprintf format specifier pads an integer with spaces to a width of 6?

A %6f

B %6d

C %06d

D %d6

The format %6d pads the integer with spaces to make it 6 characters wide.

Describe how to use sprintf in MATLAB to format a floating-point number with 4 decimal places and include it in a sentence.

Think about how to write the format string and pass the number as an argument.

Explain how to include a literal percent sign (%) in a string created by sprintf and why this is necessary.

Remember that % is used for placeholders, so you need a way to show it literally.

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