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Variables and Data Types

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In this section, we will cover the fundamental concepts of variables and data types in MUMPS. Understanding these basics is crucial for writing effective and efficient MUMPS programs.

What are Variables?

Variables are used to store data that can be manipulated and retrieved throughout the program. In MUMPS, variables do not need to be declared before they are used, and their type is determined by the context in which they are used.

Types of Variables

  1. Local Variables: These are variables that are only accessible within the current routine or block of code.
  2. Global Variables: These are variables that are accessible across different routines and sessions. They are stored in the database.

Naming Conventions

  • Variable names must start with a letter and can be followed by letters, numbers, or underscores.
  • Variable names are case-sensitive.

Example

SET name="John Doe"
SET age=30
WRITE "Name: ", name, " Age: ", age

In this example:

  • name and age are local variables.
  • SET is used to assign values to the variables.
  • WRITE is used to output the values of the variables.

Data Types

MUMPS is a dynamically typed language, meaning that variables can hold different types of data at different times. The primary data types in MUMPS are:

  1. Numeric: Represents numbers.
  2. String: Represents sequences of characters.
  3. Boolean: Represents true or false values (though not explicitly defined in MUMPS, logical operations yield boolean results).

Numeric Data Type

Numeric data types can be integers or floating-point numbers.

SET num1=100
SET num2=3.14
WRITE "Integer: ", num1, " Floating-point: ", num2

String Data Type

String data types are sequences of characters enclosed in double quotes.

SET greeting="Hello, World!"
WRITE greeting

Boolean Data Type

MUMPS does not have a dedicated boolean type, but logical operations return 1 for true and 0 for false.

SET isTrue=(5>3)
SET isFalse=(5<3)
WRITE "True: ", isTrue, " False: ", isFalse

Practical Examples

Example 1: Basic Variable Assignment

SET x=10
SET y=20
SET sum=x+y
WRITE "Sum: ", sum

Example 2: String Manipulation

SET firstName="John"
SET lastName="Doe"
SET fullName=firstName_" "_lastName
WRITE "Full Name: ", fullName

Example 3: Using Global Variables

SET ^globalVar="This is a global variable"
WRITE ^globalVar

Exercises

Exercise 1: Variable Assignment

Task: Create a MUMPS program that assigns values to three variables and prints them.

; Solution
SET var1="MUMPS"
SET var2=2023
SET var3="Programming"
WRITE "Var1: ", var1, " Var2: ", var2, " Var3: ", var3

Exercise 2: String Concatenation

Task: Write a MUMPS program that concatenates two strings and prints the result.

; Solution
SET str1="Hello"
SET str2="World"
SET result=str1_" "_str2
WRITE result

Exercise 3: Global Variable Usage

Task: Store a value in a global variable and retrieve it.

; Solution
SET ^myGlobal="Global Data"
WRITE ^myGlobal

Common Mistakes and Tips

  • Uninitialized Variables: Ensure variables are initialized before use to avoid unexpected results.
  • Case Sensitivity: Remember that variable names are case-sensitive.
  • Global Variable Naming: Use meaningful names for global variables to avoid conflicts and improve readability.

Conclusion

In this section, we covered the basics of variables and data types in MUMPS. We learned about local and global variables, numeric and string data types, and how to perform basic operations with them. Understanding these concepts is essential for progressing to more advanced topics in MUMPS programming. In the next section, we will explore basic input and output operations in MUMPS.

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