Even Odd in ALGOL 60

Welcome to the Even Odd in ALGOL 60 page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

begin
    procedure usage;
    begin
        outstring(1, "Usage: please input a number\n");
        stop
    end usage;

    comment Input a digit character from stdin and return the following:
        - "0" to "9" maps to 0 to 9
        - "+" maps to 10
        - "-" maps to 11
        - whitespace maps to 12
        - comma maps to 13
        - null byte maps to -1
        - invalid bytes map to -2;
    integer procedure indigit;
    begin
        comment Mapping:
            - "0" to "9" maps to 1 to 10
            - "+" maps to 11
            - "-" maps to 12
            - "," mapps to 13
            - "\t" maps to 14
            - "\r" maps to 15
            - "\n" maps to 16
            - " " maps to 17
            - null byte maps to 18
            - invalid byte maps 0;
        integer ch;
        inchar(0, "0123456789+-,\t\r\n ", ch);
        if ch < 1 then ch := -2
        else if ch < 14 then ch := ch - 1
        else if ch < 18 then ch := 12
        else ch := -1;
        indigit := ch
    end indigit;

    comment Input an integer from stdin into 'result' and parse it.
        The last character is read into 'ch'.
        return true if integer is valid, false otherwise;
    boolean procedure inValidInteger(result, ch);
    integer result, ch;
    begin
        boolean valid;
        integer s;

        result := 0;
        valid := false;
        s := 1;

        comment Ignore whitespace;
        for ch := indigit while ch = 12 do indigit;

        comment Process signs: ignore "+" and invert sign if "-";
    signloop:
        if ch = 10 | ch = 11 then
        begin
            if ch = 11 then s := -s;
            ch := indigit;
            goto signloop
        end;

        comment Process digits: update value;
    valueloop:
        if ch >= 0 & ch <= 9 then
        begin
            comment Invalid if overflow or underflow;
            valid := false;
            if (s > 0 & (maxint - ch) % 10 < result) |
                (s < 0 & (-1 - maxint + ch) % 10 > result) then goto done;

            result := result * 10 + s * ch;
            ch := indigit;
            valid := true;
            goto valueloop
        end;

        comment Ignore whitespace;
        for ch := ch while ch = 12 do ch := indigit;

    done:
        inValidInteger := valid
    end inValidInteger;

    boolean procedure iseven(x);
    value x;
    integer x;
    begin
        iseven := (x - 2 * (x % 2)) = 0
    end iseven;

    integer argc, result, ch;

    comment Get number of parameters. Exit if too few;
    ininteger(0, argc);
    if argc < 1 then usage;

    comment Get integer value from 1st argument. Exit if invalid or not
        end of argument;
    if !inValidInteger(result, ch) | ch != -1 then usage;

    comment Output "Even" if number is even, "Odd" otherwise;
    if iseven(result) then outstring(1, "Even")
    else outstring(1, "Odd")
end

Even Odd in ALGOL 60 was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.