Arduino Sketch Loop using Millis() - c

Question

The goal of this program is to write a string to the Arduino's LCD, and cycle between two different messages. The problem with my current version is that it cycles back and forth with no delay. How would I get these to write one at a time?
Here is the code, I left out some of the irrelevant parts:
#include <LiquidCrystal.h>
#include <string.h>
// These are the pins our LCD uses.
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
// initalize the lcd, and button input at zero.
int lcd_key = 0;
int adc_key_in = 0;
//define values for each button
#define btnRIGHT 0
#define btnUP 1
#define btnDOWN 2
#define btnLEFT 3
#define btnSELECT 4
#define btnNONE 5
// read the buttons
int read_LCD_buttons()
{
adc_key_in = analogRead(0); // detects the value from the buttons
// The buttons give values close to which values we saet them between.
if (adc_key_in > 1000) return btnNONE; // When the input is greater than 1000 that means no buttons are being pressed,
if (adc_key_in < 50) return btnRIGHT;
if (adc_key_in < 195) return btnUP;
if (adc_key_in < 380) return btnDOWN;
if (adc_key_in < 555) return btnLEFT;
if (adc_key_in < 790) return btnSELECT;
return btnNONE; // if there is some issue with values, the programs will not break.
}
void setup()
{
Serial.begin(9600); //Set the serial monitor.
lcd.begin(16, 2); //Set the LCD
}
void loop()
{
timer = millis();
if (left == true) //Right alignment
{
lcd.clear() ; //Clear any existing text
lcd.setCursor(5, 0); //Set cursor to right side.
timer = millis();
if (millis() < (timer + 5000)) {
if (show1 == true) //See if first line should be displayed. If false, nothing is displayed.
{
lcd.print("Time");
}
//Second line
lcd.setCursor(4, 1);
if (show2 == true)//See if second line should be displayed
{
lcd.print("12:00 PM");
}
}
if ((timer + 5000) > millis() < (timer + 10000)) {
//Display Date
lcd.setCursor(5, 0);
if (show1 == true)//See if first line should be displayed.
{
lcd.print("Date");
}
//Second line
lcd.setCursor(1, 1);
if (show2 == true)//See if second second should be displayed.
{
lcd.print("Nov. 16, 2012");
}
}
}
}

Answer 1

This condition if ((timer + 5000) > millis() < (timer + 10000)) makes no sense in C - at least it don't do what you are expecting.
It is invoked like below:
first (timer + 5000) > millis() is invoked and its value is 0 or 1
next 0 or 1 (from first condition) is compared with (timer + 10000) which is always true (assuming that you have not overflow time value and you are not comparing with large negative number)
You should use something like if ((timer + 5000) > millis() && mills() < (timer + 10000)) or rather:
int hlp_time = millis();
if ((timer + 5000) > hlp_time && hlp_time < (timer + 10000))
since time returned by millis() will vary between each check in if condition.

Answer 2

Have you tried setting timer = millis(); to outside the loop?