String formatting (sprintf) in MATLAB - Mini Project: Build & Apply

String formatting (sprintf)

📖 Scenario: You are creating a simple program to format a message that shows a person's name and age in a nice sentence.

🎯 Goal: Build a MATLAB program that uses sprintf to create a formatted string showing a person's name and age.

📋 What You'll Learn

Create variables for name and age with exact values

Create a format string variable for sprintf

Use sprintf with the format string and variables

Print the formatted string

💡 Why This Matters

🌍 Real World

Formatting strings is useful when creating messages, reports, or logs that combine text and numbers clearly.

💼 Career

Many programming jobs require creating readable output or reports, and knowing how to format strings is a key skill.

1

Create variables for name and age

Create a variable called name and set it to 'Alice'. Create a variable called age and set it to 30.

MATLAB

% Your code here

Hint

Use single quotes for strings in MATLAB, like 'Alice'.

2

Create a format string for sprintf

Create a variable called formatStr and set it to 'My name is %s and I am %d years old.'.

MATLAB

name = 'Alice';
age = 30;
% Your code here

Hint

The format string uses %s for strings and %d for integers.

3

Use sprintf to create the formatted message

Create a variable called message and set it to the result of sprintf(formatStr, name, age).

MATLAB

name = 'Alice';
age = 30;
formatStr = 'My name is %s and I am %d years old.';
% Your code here

Hint

Call sprintf with the format string and variables in order.

4

Print the formatted message

Use disp(message) to display the formatted message.

MATLAB

name = 'Alice';
age = 30;
formatStr = 'My name is %s and I am %d years old.';
message = sprintf(formatStr, name, age);
% Your code here

Hint

Use disp to print the string stored in message.

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