Local Variables

Local Variables

uCalc lets you define variables that are local to an expression.� The definition is done within the expression itself.� If a variable with the same name was already defined, the local variable will not interfere with the previously defined variable of the same name.� A local variable can hold a separate value from the previously defined variable.� An expression can have any number of local variables, separated by commas.

Example 1: Multiple local variables in an expression

This example uses two local variables: x, and y.� After the expression is finished, x reverts to being undefined, and y still has its original value of 123, which it had before the expression was evaluated.

Visual Basic

ucDefineVariable "y = 123"

Print ucEvalStr("Local(x, y, (uc_For(x, 1, 5, 1, SetVar(y, y+x^2)); y))") ' Returns 55

Print ucEvalStr("x") ' Returns an error: Undefined identifier

Print ucEvalStr("y") ' Returns 123

Example 2:� Local variable, and ByHandle argument (Summation)

This example defines a summation routine named Sum().� The actual callback function is named Sum_(), and requires 5 arguments, where the last one is a variable passed ByHandle.� A syntax construct named Sum() is defined so that the last two arguments are optional.� The last argument is made local.� If omitted it defaults to a variable named x.� By making it local you don't have to worry about defining a variable ahead of time for use with Sum().� Plus it will not interfere with another variable of the same name, whether it is outside the expression, or Sum is nested several times within the same expression.� Expressions such as the following can be entered:

Sum(x^2, 1, 10)�� ' returns 385

Sum(n+5, 1, 25, 1, n)�� ' returns 450

Sum(Sum(x^2, 1, 10)*10, 1, 5) ' returns 19250

Visual Basic

' The following 3 lines can be placed in Form_Load()

ucDefineFunction "Native: Sum_(ByExpr Expr, Start, Finish, Step, ByHandle Var)", AddressOf ucSum

ucDefineSyntax "Sum({Expr}, {Start}, {Finish} [, {Step=1} [, {Var=x}]])" _

�� + "::= Local({Var}, Sum_({Expr}, {Start}, {Finish}, {Step}, {Var}))"

' The following callback routine goes in a separate module, such as DemoVB.Bas

Sub ucSum(ByVal Expr As Long)

�� Dim Expression As Long, VarHandle As Long

�� Dim Start As Long, Finish As Long, sStep As Long

�� Dim x As Double, Total As Double

�� Expression = ucArgHandle(Expr, 1)

�� Start = ucArg(Expr, 2)

�� Finish = ucArg(Expr, 3)

�� sStep = ucArg(Expr, 4)

�� VarHandle = ucArgHandle(Expr, 5)

�� For x = Start To Finish Step sStep

�� ucSetVariableValue VarHandle, x

�� Total = Total + ucEvaluate(Expression)

�� Next

�� ucReturn Expr, Total

End Sub

This same example is also found in the source code for the demo program for C#, C++ Builder, PB, VB (classic), VB.NET, and VC++.

Example 3:� Local variable, and ByHandle argument (Equation Solver)

The concept in this example is very similar to that of the previous example.� This routine is a simple equation solver based on an adaptation of the bisection method algorithm.� This code is just enough to get you started.� You will want to add to it for a more robust solver.� Here are examples of equations it can solve:

Solve(x^2 + 1 = 26)�� ' returns� 5

Solve(x^2 + 1 = 26, -1000, 0) ' returns -5

Visual Basic

' The following lines can be placed in Form_Load()

ucDefineFunction "Native: Solve_(ByExpr Expr, a, b, ByHandle Var)", AddressOf ucSolve

ucDefineSyntax "Solve({Expr} [, {a=-100000000} [, {b=100000000} [, {Var=x}]]]) " _

�� + "::= Local({Var}, Solve_({Expr}, {a}, {b}, {Var}))"

ucDefineSyntax "Solve({Left} = {Right} [, {etc}]) ::= Solve({Left}-({Right}) {etc: , {etc}})"

' The following callback routine goes in a separate module, such as DemoVB.Bas

Sub ucSolve(ByVal Expr As Long)

�� Dim Expression As Long, Variable As Long, Iterations As Long

�� Dim a As Double, b As Double, fa As Double, fb As Double

�� Dim Value As Double, tmp As Double

�� Expression = ucArgHandle(Expr, 1)

�� a = ucArg(Expr, 2)

�� b = ucArg(Expr, 3)

� �Variable = ucArgHandle(Expr, 4)

�� ucSetVariableValue Variable, a: fa = ucEvaluate(Expression)

�� ucSetVariableValue Variable, b: fb = ucEvaluate(Expression)

��

�� If fb < fa Then tmp = a: a = b: b = tmp�� 'swap a, b

��

�� Do While Abs(b - a) > 0.000000000000001

�� ucSetVariableValue Variable, (a + b) / 2

��

�� Value = ucEvaluate(Expression)

��

�� If Value = 0 Then a = (a + b) / 2: Exit Do

�� If Value < 0 _

�� Then a = (a + b) / 2 _

�� Else b = (a + b) / 2

�� Iterations = Iterations + 1

�� If Iterations = 100 Then Exit Do

�� Loop

��

�� If Abs(Value) > 0.0000000001 Then ucRaiseErrorMessage Expr, "Solution not found"

�� ucReturn Expr, a

End Sub

This same example is also found in the source code for the demo program for C#, C++ Builder, PB, VB (classic), VB.NET, and VC++.