README.md

COBOL Terminal Cursor Control Demo

This is a small experimental COBOL project I built to learn a little bit about COBOL. The goal was simple: see if COBOL could support basic interactive console behavior—specifically, moving an asterisk around the screen using the W/A/S/D keys.

It uses raw ANSI escape sequences for cursor control and a small C helper to handle non-blocking keyboard input (so the user doesn't have to press Enter). The original version got stuck in a classic AI rehash loop—ChatGPT kept giving plausible but ineffective tweaks. I revisited it later using the five Sens-AI habits (Context, Research, Problem Framing, Refining, and Critical Thinking), and that broke the loop and got everything working.

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🔧 How to Build and Run

Make sure you have:

• A terminal that supports ANSI escape codes
• cobc (from GNU COBOL)
• gcc

Steps:

# Compile the C helper to capture raw keyboard input (without pressing enter)
gcc -fPIC -shared -o libgetch.so getch.c

# Compile and link the COBOL program with the C object file
cobc -x -o move-asterisk-raw move-asterisk-raw.cob -L. -lgetch

# Run the resulting binary
./move-asterisk-raw

The program should clear the screen and allow you to move the asterisk using the W, A, S, and D keys—without needing to hit Enter.

getch.c

#include <termios.h>
#include <unistd.h>

void getch(char *out) {
    struct termios oldt, newt;
    char ch;

    tcgetattr(STDIN_FILENO, &oldt);          // Save current terminal settings
    newt = oldt;
    newt.c_lflag &= ~(ICANON | ECHO);        // Disable canonical mode and echo
    tcsetattr(STDIN_FILENO, TCSANOW, &newt); // Apply new settings

    read(STDIN_FILENO, &ch, 1);              // Read one character

    tcsetattr(STDIN_FILENO, TCSANOW, &oldt); // Restore original settings
    *out = ch;                               // Pass back to COBOL
}

move-asterisk-raw.cob

       IDENTIFICATION DIVISION.
       PROGRAM-ID. MoveAsteriskRaw.

       DATA DIVISION.
       WORKING-STORAGE SECTION.

       01 ROW             PIC 99 VALUE 10.
       01 COL-VALUE       PIC 99 VALUE 10.
       01 INPUT-KEY       PIC X.
       01 LOOP-FLAG       PIC X VALUE "Y".
       01 ROW-STR         PIC 99.
       01 COL-STR         PIC 99.
       01 CURSOR-CODE     PIC X(20).
       01 ESCAPE-SEQ      PIC X VALUE X"1B".
       01 CLEAR-CODE      PIC X(10).

       PROCEDURE DIVISION.

       MAIN-LOOP.
           PERFORM UNTIL LOOP-FLAG = "N"
               *> Clear the screen
               STRING ESCAPE-SEQ "[2J"
                   DELIMITED BY SIZE INTO CLEAR-CODE
               DISPLAY CLEAR-CODE NO ADVANCING

               *> Move the cursor and draw the asterisk
               PERFORM SHOW-ASTERISK

               *> Display instructions at a fixed position
               DISPLAY ESCAPE-SEQ "[22;1H" NO ADVANCING
               DISPLAY "Use W/A/S/D to move, Q to quit."

               *> Get one raw character from the user
               CALL "getch" USING INPUT-KEY

               *> Interpret movement
               EVALUATE FUNCTION UPPER-CASE(INPUT-KEY)
                   WHEN "W"
                       IF ROW > 1
                           SUBTRACT 1 FROM ROW
                       END-IF
                   WHEN "S"
                       IF ROW < 20
                           ADD 1 TO ROW
                       END-IF
                   WHEN "A"
                       IF COL-VALUE > 1
                           SUBTRACT 1 FROM COL-VALUE
                       END-IF
                   WHEN "D"
                       IF COL-VALUE < 20
                           ADD 1 TO COL-VALUE
                       END-IF
                   WHEN "Q"
                       MOVE "N" TO LOOP-FLAG
               END-EVALUATE
           END-PERFORM

           DISPLAY ESCAPE-SEQ "[23;1H"
           DISPLAY "Goodbye!"
           STOP RUN.

       SHOW-ASTERISK.
           MOVE ROW TO ROW-STR
           MOVE COL-VALUE TO COL-STR
           STRING
               ESCAPE-SEQ "[" DELIMITED BY SIZE
               ROW-STR DELIMITED BY SIZE
               ";" DELIMITED BY SIZE
               COL-STR DELIMITED BY SIZE
               "H" DELIMITED BY SIZE
               INTO CURSOR-CODE
           DISPLAY CURSOR-CODE NO ADVANCING
           DISPLAY "*" NO ADVANCING.