Your first stateful script

smallest-useful-script.gpc

int enabled;

main {
    if(event_press(PS5_CROSS)) {
        enabled = !enabled;
    }

    if(enabled) {
        set_val(PS5_R1, 100);
    }
}

This introduces the four ideas used by almost every real script:

Element	Description
int enabled;	Declares a global signed 32-bit runtime variable. It starts at 0.
event_press	Is true for the cycle in which the input transitions from released to pressed.
!enabled	Changes zero to one and any nonzero value to zero.
State	State set in one cycle remains available in later cycles until the script reloads or code changes it.