Differences between Expressions and Statements
To introduce the expressions and statements (syntactic entities) in FreeBASIC.
Preamble:
Simply put, an expression represents a value and a statement represents an operation.
However, in fact, some special expressions may be composed and represent multiple values, and some statements may be composed of several sub operations/statements.
By context, some statements can also be considered expressions.
Statements can contain other constructs such as expressions, keywords, operators, and other elements.
Expressions are parts of statements that return values. Thus, expressions can be used whenever a value is expected.
The following description does not make very precise definitions for expressions and statements. It is difficult to achieve this.
Not all types of expressions and statements are covered here, but only simple examples are highlighted.
However, in fact, some special expressions may be composed and represent multiple values, and some statements may be composed of several sub operations/statements.
By context, some statements can also be considered expressions.
Statements can contain other constructs such as expressions, keywords, operators, and other elements.
Expressions are parts of statements that return values. Thus, expressions can be used whenever a value is expected.
The following description does not make very precise definitions for expressions and statements. It is difficult to achieve this.
Not all types of expressions and statements are covered here, but only simple examples are highlighted.
Expressions
An expression is a collection of one or more terms that can perform a mathematical or logical operation. To be precise, an expression must have at least one operand but may not have any operator.
The terms are usually either literals or variables or functions that are combined with operators to evaluate for example to a string or numeric result or boolean or user defined type.
A value in itself is a simple expression, just like a variable. Evaluating a variable gives the value to which the variable refers.
Expressions can be used to perform calculations, manipulate variables, or concatenate strings.
Expressions are evaluated according to precedence order. Use parentheses to override the default precedence order.
The terms are usually either literals or variables or functions that are combined with operators to evaluate for example to a string or numeric result or boolean or user defined type.
A value in itself is a simple expression, just like a variable. Evaluating a variable gives the value to which the variable refers.
Expressions can be used to perform calculations, manipulate variables, or concatenate strings.
Expressions are evaluated according to precedence order. Use parentheses to override the default precedence order.
Statements
A statement is a basic unit of execution of a program. A statement is a complete instruction in FreeBASIC programs.
It may contain keywords, operators, variables, literal values, constants and expressions.
Statements could be categorized as:
It may contain keywords, operators, variables, literal values, constants and expressions.
Statements could be categorized as:
- Declaration statements: these are the statements where the user names a variable, constant, or procedure, and can also initialize it.
- Executable statements: these are the statements which initiate actions. These statements can call a procedure, loop or branch through blocks of code or assign values or expression to a variable or constant. In the last case, it is called an expression statement. The most common expression statements are assignments and function calls.
A statements normally takes up one line with no terminator character, but:- Executable statements: these are the statements which initiate actions. These statements can call a procedure, loop or branch through blocks of code or assign values or expression to a variable or constant. In the last case, it is called an expression statement. The most common expression statements are assignments and function calls.
- several statements can also be stacked on a same line by using the separator character, a colon (:) to delimit them,
- or a statement may also be continued to the next line using the continuation character, an underscore (_) to extend the statement from one line to the next.
- or a statement may also be continued to the next line using the continuation character, an underscore (_) to extend the statement from one line to the next.
Basic examples of expressions / statements
Some basic examples just to illustrate the definitions above.
Basic examples of expressions
Basic examples of expressions
- Arithmetic expression:
Basic examples of statements
10
- String expression:
this is an expression that is evaluated to the numeric value 10.
10 + 13
this is another expression that is evaluated to produce the numeric value 23.
"hello"
- Combined expression:
evaluates to the string "hello".
"hello" & " " & "world"
evaluates to the string "hello world".
Len("hello" & " " & "world")
- Logical expression:
Len function evaluating the length of the string expression.
10 > 9
evaluates to boolean value true (more precisely produces the integer value -1 here).
10 < 20
evaluates to boolean value false (more precisely produces the integer value 0 here).
true
evaluates to boolean value true.
a=20 And b=30
evaluates to true (-1) or false (0) based on the values of a and b.
- Statement:
Print 10 + 13
Print "hello" & " " & "world"
- Assignment statement:Print "hello" & " " & "world"
where the arguments of the two Print statements are expressions listed above.
average = 55 + 33
- Declaration statement with initializer:
where the right-hand-side is an expression.
Dim As Integer I = J + 3
- Conditional statement:
where the right-hand-side of the initializer is an expression.
If (expression) Then
statement 1
Else
statement 2
End If
if the expression following the If statement evaluates to a truth value, statement 1 is executed else statement 2 is executed.
See also:
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