What type of operator can be used to determine whether a specific relationship exists between two values?

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Addition [+]

Description
This operator provides the sums of two numbers. Basic arithmetic operator used for addition; the result of an arithmetic operator is usually a numeric value.

Syntax
[expression1] [expression2]

Comments
Although the + operator can be used to concatenate two character strings, the & operator should be used for concatenation to eliminate ambiguity and provide self-documenting code. If + operator is used, there may be no way to determine whether addition or string concatenation will occur. The underlying subtype of the expressions determines the behavior of the + operator in the following way:

If

Then

If one or both expressions are Null expressions, the result is Null. If both expressions are Empty, the result is an integer subtype. However, if only one expression is Empty, the other expression is returned unchanged as a result.

Example

READ {.ProjectsSampleSample.prj}:Oswego DEFINE Newvar NUMERIC ASSIGN Newvar = Age + 5 LIST Age Newvar

ARITHMETIC

Description
These basic arithmetic operators can be used in combination with other commands. The result is a numeric value.

Syntax
[Expression] [Expression]

• [Expression] is a numeric value or a variable containing data in numeric format.

Comments
The results are expressed in numeric format. The basic mathematical operators that can be used in Epi Info are as follows:

• Addition + Basic arithmetic operator used for addition; the result of an arithmetic operator is usually a numeric value [i.e., EX. 3 + 3].
• Subtraction – [Used for subtraction or negation.] Basic arithmetic operator used for subtraction or negation; the result of an arithmetic operator is usually a numeric value [i.e., EX. 3 – 1].
• Multiplication * [Asterisk] Basic arithmetic operator used for multiplication; the result of an arithmetic operator is usually a numeric value.
• Division / Basic arithmetic operator used for division; the result of an arithmetic operator is usually a numeric value.
• Exponentiation ^
• Modulus or Remainder MOD

Arithmetic operators are shown in descending order of precedence. Parentheses can be used to control the order in which operators are evaluated. The default order, however, frequently achieves the correct result.

While it is possible to do date math with dates considered as a number of days [e.g., IncubationDays = SymptomDateTime – ExposureDateTime], the behavior of the database services underlying Epi Info makes it more efficient to use time interval functions [e.g., IncubationDays = MINUTES[ExposureDateTime, Symptom DateTime]/[24*60]]. For doing date math, the following rules apply:

Date + Date produces Date
Date – Date produces Days
Date * Date not permitted
Date / Date not permitted
Date ^ Date not permitted
Date + Number produces Date
Number + Date produces Number
The last two rules apply as well to other math operations: -, *, /, ^
The “zero day” for date math is December 30, 1899.

Example

READ {.ProjectsSampleSample.prj}:Surveillance DEFINE var1 NUMERIC ASSIGN var1=1250 MOD 100 DEFINE var2 NUMERIC ASSIGN var2=1+1 DEFINE var3 NUMERIC ASSIGN var3=2-1 DEFINE var4 NUMERIC ASSIGN var4=1*1 DEFINE var5 NUMERIC ASSIGN var5=8/4 DEFINE var6 NUMERIC ASSIGN var6=5^2 LIST var1 var2 var3 var4 var5 var6

Comparisons

Description
These comparison operators can be used in If, Then, and Select statements in Check Code and Analysis programs. Yes/No variables can only be tested for equality against other Yes/No constants [+], [-], and [.].

Operator

Description