Arithmetic expressions

When no parentheses are present, arithmetic expressions are evaluated from left to right, with multiplication and division having a higher priority than addition and subtraction.

Highest NOT, - (unary)
*, /, MOD
+, -
<, โ‡, >, =, >=, >
Lowest AND, OR, XOR

The arithmetic operators, +, -, *, and /, work in the expected fashion, however, the result of arithmetic on type BYTE, WORD or INT cannot have a fractional result. Therefore 5 / 2 evaluates as 2, not 2.5. However, 5.0 / 2.0 evaluates as 2.5, because the presence of the decimal point tells the compiler that the numbers are of type FLOAT.

PRINT 5/2 ' Outputs 2
PRINT 5.0/2.0 ' Outputs 2.5

Operators, except unary operators, accept two operands. These two operands do not have to be of the same type. In a mixed expression, the operands are promoted to the higher type, being BYTE the lowest and FLOAT the highest type. The table below summarizes the results of a partially evaluated expression.

BYTE WORD INT FLOAT
BYTE BYTE WORD INT FLOAT
WORD WORD WORD INT FLOAT
INT INT INT INT FLOAT
FLOAT FLOAT FLOAT FLOAT FLOAT

The type of the data being operated on must be considered. For example, adding two values of type BYTE will always result in a value which is also of type BYTE, even if the result is too large to fit in a BYTE. For example, if x is a variable of type BYTE which has been previously assigned the value of 254, then the expression x + 4 will NOT have a value of 258, but 2. This is because BYTE variables can only take on values between 0 and 255, so that when you add 4 to 254, the result is (258-256) = 2.

Likewise, adding or multiplying two numeric literals is subject to overflow, even if the left hand side of the assignment is a variable that could otherwise fit the result.

DIM a AS INT
a = 250 + 6
PRINT a ' Outputs 0

Since both 250 and 6 are of type BYTE, the result will also be of type BYTE, regardless the type of a. To overcome this problem, use the typecasting functions CBYTE, CWORD, CINT and CFLOAT.

DIM a AS INT
a = CINT(250) + CINT(6)
PRINT a ' Outputs 256