How to fix run-time error 201

Question

help me, please. I don't know how to fix this error.

Program Polynomial;

type
    arrayOfInt = Array[1..21] of Integer;
    biggerArrayOfInt = Array[1..41] of Integer;

function isNumber(c : Char): Boolean;
var
    res : Boolean;
    code : Longint;
begin
    code := Ord(c);
    if ((code > 47) AND (code < 58)) then begin
        res := true
    end
    else
    begin
        res := false;
    end;
    isNumber := res;
end;

function parsePolynomial(polynomial : String): arrayOfInt;
var
    coeficients : Array[1..21] of Integer;
    number : Integer;
    coef : Integer;
    tmp : String;
    i, j : Integer;
    positive : Boolean;
    numberPosition, numberLength : Integer;
    expectX : Boolean;
begin
    i := 1;
    for j:=1 to Length(coeficients) do
    begin
        coeficients[j] := 0;
    end;
    while (true) do
    begin
        coef := 0;
        number := 0;
        positive := true;
        expectX := true;
        if(polynomial[i] = '-') then begin
            positive := false;
            i := i + 1;
        end;
        if(polynomial[i] = '+') then begin
            i := i + 1;
        end;
        if(isNumber(polynomial[i])) then begin
            numberPosition:= i;
            while (isNumber(polynomial[i])) do
            begin
                i := i + 1;
            end;
            tmp := Copy(polynomial, numberPosition, i - numberPosition);
            Val(tmp, number);
            if(not positive) then begin
                number := number * -1;
            end;

            if ((not(polynomial[i] = '*')) OR (i > length(polynomial))) then
                    begin
                expectX := false;
            end
            else
            begin
                i:= i + 1;
            end;
        end
        else
        begin
            if(positive) then begin
                number := 1;
            end
            else
            begin
                number := -1;
            end;
        end;

        if (expectX) then begin
            if(not(polynomial[i] = 'x')) then begin
                write('Bad input!');
                exit;
            end
            else
            begin
                i := i + 1;
                if (polynomial[i] = '^') then begin
                    i := i + 1;
                    if (not isNumber(polynomial[i])) then begin
                        write('Bad input!');
                        exit;
                    end;
                    numberPosition:= i;
                    while (isNumber(polynomial[i])) do
                    begin
                        i := i + 1;
                    end;
                    tmp := Copy(polynomial, numberPosition, i - numberPosition);
                    Val(tmp, coef);
                end
                else
                begin
                    coef := 1;
                end;
            end;
        end;

        coeficients[coef + 1] := number;

        if ((length(polynomial)) - 1 < i) then begin
            break;
        end;
    end;
   parsePolynomial := coeficients;
end;

function sumPolynomial(polynomial1, polynomial2 : array of Integer): arrayOfInt;
var
    coeficients : Array[1..21] of Integer;
    i : Integer;
begin
    for i := Length(polynomial1) downto 0 do
    begin
        coeficients[i+1] := polynomial1[i] + polynomial2[i];
    end;
    sumPolynomial := coeficients;
end;

function productOfPolynomial(polynomial1, polynomial2 : array of Integer): biggerArrayOfInt;
var
    coeficients : Array[1..41] of Integer;
    i, j : Integer;
begin
    for j:=1 to Length(coeficients) do
    begin
        coeficients[j] := 0;
    end;
    for i := Length(polynomial1) downto 0 do
    begin
        for j := Length(polynomial2) downto 0 do
        begin
                coeficients[i+j+1] := coeficients[i+j+1] + polynomial1[i] * polynomial2[j];
        end;
    end;
    productOfPolynomial := coeficients;
end;

function substractOfPolynomial(polynomial1, polynomial2 : array of Integer): arrayOfInt;
var
    coeficients : Array[1..21] of Integer;
    i : Integer;
begin

    for i := Length(polynomial1) downto 0 do
    begin
        coeficients[i+1] := polynomial1[i] - polynomial2[i];
    end;

   substractOfPolynomial := coeficients;
end;


procedure printPolynomial(polynomial: array of Integer);
var 
    i : Integer;
    isFirst : Boolean;
    isZero : Boolean;
begin
    isFirst := true;
    isZero := true;
    for i := length(polynomial) downto 0 do
    begin
        if polynomial[i] <> 0 then begin
            isZero := false;
            if((not isFirst) AND (polynomial[i] > 0)) then begin
                write('+');
            end;
            if((polynomial[i] = -1)) then begin
                write('-');
            end;
            if(((polynomial[i] > 1) OR (polynomial[i] < -1)) OR ((i = 0) AND not(polynomial[i] = 0))) then begin
                write(polynomial[i]);
                if((i > 0)) then begin
                    write('*');
                end;
            end;

            if(i > 0) then begin
                write('x');
                isFirst := false;
                if (i > 1) then begin
                    write('^', i);
                end;
            end;
            write()
        end;
    end;
    if (isZero) then begin
        write(0);
    end;

end;

var
    polynomial1, polynomial2, result: Array[1..21] of Integer;
    polynomialInput: String;

begin
    readln(polynomialInput);
    polynomial1 := parsePolynomial(polynomialInput);

    readln(polynomialInput);
    polynomial2 := parsePolynomial(polynomialInput);

    printPolynomial(sumPolynomial(polynomial1, polynomial2));
    writeln('');
    printPolynomial(substractOfPolynomial(polynomial1, polynomial2));
    writeln('');
    printPolynomial(productOfPolynomial(polynomial1, polynomial2));
end.

Answer 1

Runtime error 201 means range check error. Quick glance over the source code makes me suspect that somewhere some operation returns a value that doens't fit in integer range (-32786..32767 in FreePascal by default). Easiest solution would be to use a larger datatype for example longint (roughly between -2*10^9..2*10^9) or int64 (~9*10^18..9*10^18).

If you use command line compiler using -gl command line option would display line numbers in run-time error backtraces. This would make it easier for you to pinpoint the issue.