User-Controlled Input and Output in MATLAB

Objectives of Chapter 7

  • Demonstrate how to prompt the user for input in M-files.

  • Review and utilize output functions: disp, fprintf, and sprintf for formatted outputs.

  • Create and manage tables using the table function.

  • Apply graphical methods for user program input and output.

User-Controlled Input and Output

User Defined Input

  • Hard-coded values have previously been used in M-files.

  • The input function allows dynamic prompting for user input in M-files.

  • This allows for flexibility depending on user input each time the program runs.

Input Types

  • Acceptable data types:

    • Scalars

    • Arrays: Enter values inside square brackets.

    • Character strings: Enter within single quotes (' ').

    • Optionally specify string input by using ‘s’.

Practice Exercise

  • Engage in hands-on activities that reinforce the understanding of input types in MATLAB.

Output Options

Display Output with disp Function

  • Use the disp function to display array contents, without printing the variable name.

  • Capable of showing strings as well.

  • Combine multiple disp calls for structured output, though each will appear on a new line.

  • Example:

disp(['The values in the x array are: ', num2str(x)])

  • To include an apostrophe inside a string, double it (e.g., 'The moon''s gravity').

Formatted Output with fprintf Function

  • fprintf provides extensive control over how the output format is displayed.

  • Capable of combining text with numeric values and controlling precision and formatting.

  • Usage:

fprintf('format_specifications', variables);

  • Placeholders are important to format the output correctly:

    • %f: floating-point number,

    • %d: integer,

    • %s: string, etc.

  • Example of using formatted output:

fprintf('x = %5.2f
', x);
Formatted Output to Files

  • Open a writable file to output data using the fprintf function combined with a file identifier.

  • Automatically counts characters output to the specified file.

Using sprintf for String Storage

  • sprintf functions similarly to fprintf, but it stores the output string for use later in the program.

  • Useful for annotating graphs or other dynamic contents in your code.

Example of sprintf Use

  • ```matlab
    myString = sprintf('The current temperature is %d degrees', temperature);

---

## Table Creation
- The **table** function enables the combination of different data types (text and numeric) into a single table format.
- Syntax example:

matlab
table(variable1, variable2, …);

- All arguments must be column vectors for proper table formatting.

---

## Graphical Input Techniques
- **ginput** function allows users to click on a graph to retrieve **x-y ordered pairs**.
- Displays a floating crosshair during interaction.
- Example usage:

matlab
[x, y] = ginput(n);

- Retrieves **n** ordered pairs based on user clicks.

### Adding Text with gtext
- **gtext** allows placing text at a specified graph location, making interaction more intuitive.
- Usage example:

matlab
gtext('Label');
```

Importing and Exporting Data

  • MATLAB supports multiple data formats including .txt, .xls, and .jpg for reading and writing.

  • The load command is suitable for .mat or .dat files.

  • Specialized write commands exist for Excel (like writematrix) which allow for saving matrices directly to an Excel file.

Debugging Tools in MATLAB

  • Essential tools include the Code Analyzer, Breakpoints, and Error Highlighting features to assist in finding bugs in code.

  • Debugging methods enhance the user's ability to fix code errors efficiently.

Common Debugging Tips

  • Remember to include formatting specifiers in fprintf; missing them often leads to silent failures without explicit errors.

Summary of Key Functions

  • Input Function: Facilitates user data entry dynamically.

  • disp Function: Quick display without modification of the output format.

  • fprintf Function: Advanced formatted printing capabilities.

  • sprintf Function: Stores formatted strings for later use.

  • ginput Function: Graphical input retrieval.

  • table Function: Creates structured outputs with differing data types.

Overall, this chapter emphasizes the importance of interactive input/output management in enhancing user experience with MATLAB applications.