// Make the soldiers who aren't patrolling attack the enemy
for (int i = NUM_SOLDIERS / 2; i < NUM_SOLDIERS; ++i) {
    auto &soldier = state.soldiers[i];
    if (soldier.hp == 0) // If this soldier is dead, skip it
        continue;

    for (auto enemy_soldier : state.enemy_soldiers) {
        if (enemy_soldier.hp != 0) { // Ensure your prospective target has
                                     // not already been slain
            soldier.soldier_target = enemy_soldier.id;
            break;
        }
    }
}