Variable or identifier is required to store data. One variable can store only one type of data. It can store only one value (data item) at a time. But, we can always change the value of the variable throughout the program without changing its data type.
To store data (input, intermediate results, output), we need variables (or containers). To use variables in our program, we need to declare the variables:
Variable declaration:
1. Choose the appropriate data type for the variable
2. Specify a legitimate and unique name for the variable.
Naming rules for variables:
1. Must start with a letter or underscore( _ )
2. Second and subsequent characters can be alpha numeric
3. Do not use any special characters or punctuation marks including space
4. Do not use any key words or reserved words for naming variables; Ex: String, integer, me, if, loop, else- you will see the key words in blue color.
5. Choose a name that reflects the content for the variable
Examples:
1) A1 as the variable name: valid but does not reflect the content 2) 3TestScores - Not valid because it starts with a number midTermTestScore - camel casing convention is followed to name the variables. Capitalize the first letter of second and subsequent words in the variable's name. This is not syntax and the compiler does not give an error if camel casing is not followed. This is for our own reading and documentation purposes.
Data types:
1. Numeric a. Integer Ex: 2, 5, -10, -21, 0 b. Decimal Ex: 1.56, 8.456,-3.2
2. Text a. Single letter - Character b. Multi letter - String
3. Alphanumeric – String
4. Boolean – True or false
Visual logic is case sensitive: testScore, TESTSCORE, TeStScOre, testscore refer to different variables.

Variable declaration:
1.integer testScore
This statement declares testScore variable as of Integer data type. It assigns 0 to testScore since we did not set any value for testScore
2. string studentName declares studentName as of String data type variable
Assigning a value to a variable:
To assign 90 to testScore variable, you type: testScore = 90
'=' sign is the assigning operator. It assigns the right side value to the left side variable.
Assigning operator "=" rules:
1. Always use the variable that needs to be assigned on the left side of "=" operator
2. On the right side, you may have a value such as a number or a name or you may have another pre defined variable or you may have any valid arithmetic expression.
Examples: testScore = 80 - valid
75 = testScore - Invalid because the variable has to on the left side and the value has to be on the right side. testScore = score1 - valid provided score1 is defined prior to this statement testScore = score1 + score2 - score3 valid provided score1, score2 and score3 are defined prior to this statement.