表达式的类型必须是布尔值

if (condition) {
  element.style.display = 'block';
} else {
  element.style.display = 'none';
}

boolean isEmpty = (str == null || str.isEmpty());

SELECT * FROM table WHERE field IS NULL;

if [ -e file ]; then
  echo "File exists"
else
  echo "File does not exist"
fi

status:
  conditions:
  - lastProbeTime: null
    lastTransitionTime: 2022-01-01T00:00:00Z
    status: "True"
    type: Initialized
  - lastProbeTime: null
    lastTransitionTime: 2022-01-01T00:00:00Z
    status: "True"
    type: Ready
  - lastProbeTime: null
    lastTransitionTime: 2022-01-01T00:00:00Z
    status: "True"
    type: ContainersReady
  - lastProbeTime: null
    lastTransitionTime: 2022-01-01T00:00:00Z
    status: "True"
    type: PodScheduled

if (connect(socket_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == 0) {
  printf("Connection established\n");
} else {
  printf("Connection failed\n");
}

iptables -A INPUT -p tcp --dport 80 -j ACCEPT

if (decode_frame() == 0) {
  printf("Frame decoded\n");
} else {
  printf("Frame decode failed\n");
}

if process_frame(frame):
  print("Frame processed")
else:
  print("Frame processing failed")

if model.train():
  print("Model trained")
else:
  print("Model training failed")

if device.is_connected():
  print("Device connected")
else:
  print("Device disconnected")

if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS) == PackageManager.PERMISSION_GRANTED) {
  // Permission granted
} else {
  // Permission denied
}

if df -h / | awk '{print $5}' | grep -q "100%"; then
  echo "Disk full"
else
  echo "Disk not full"
fi

if (transaction.confirmations >= 3) {
  console.log("Transaction confirmed");
} else {
  console.log("Transaction not confirmed");
}

if (Physics.Raycast(ray, out hit, 100.0f)) {
  Debug.Log("Hit target");
} else {
  Debug.Log("Missed target");
}