For Task #2, I did an implementation of the shunting yard method. It can evaluate valid infix expressions and it will evaluate invalid ones too since there is no validity checking.
Function Eval(Expr)
var OpChar = [ "(", "*", "+", "-", ")" ]
var OpPrec = [ 4, 3, 2, 2, 1 ]
float VS[0] int TopVS = 0 // Value Stack
int OS[0] int TopOS = 0 // Operator Stack
Expr += "+0" // This makes it finish up the stuff on
int I // the stack when it gets to the end
For I = 0 To Len(Expr) Loop
int J = ChrVal(Expr[I]) - ChrVal("(")
If J < 64 And 1 << J & 0x2F Then // Expr[I] ~ "()+-*"
J = [ 0, 4, 1, 2, -1, 3 ][J] // Remap the character code
While TopOS > 0 Loop
If OpPrec[J] > OpPrec[OS[TopOS - 1]] Then Break EndIf
If OpChar[OS[TopOS - 1]] == "(" Then
TopOS -= OpChar[J] == ")" // Pop matching '()'
Break
EndIf
TopOS -= 1 // Evaluate the operator on top
If OpChar[OS[TopOS]] == "+" Then
TopVS -= 1
VS[TopVS - 1] += VS[TopVS]
EndIf
If OpChar[OS[TopOS]] == "-" Then
TopVS -= 1
VS[TopVS - 1] -= VS[TopVS]
EndIf
If OpChar[OS[TopOS]] == "*" Then
TopVS -= 1
VS[TopVS - 1] *= VS[TopVS]
EndIf
Repeat
If OpChar[J] != ")" Then
OS[TopOS] = J
TopOS += 1
EndIf
Else
int J
For J = I To Len(Expr) Loop
int N = ChrVal(Expr[J]) - 46 // Expr[J] !~ ".0123456789"
If N > 63 Or 1 << N & 0xFFD == 0 Then Break EndIf
Repeat
If J > I Then // It is a Number
J -= 1
VS[TopVS] = Float(Expr[I: J])
TopVS += 1
I = J
EndIf
EndIf
Repeat
Return VS[0]
