Flag to print plots

Question

In my script I'm printing multiple plots separately. Something like:

library(ggplot2) 

mtcars$gear <- factor(mtcars$gear,levels=c(3,4,5),
                      labels=c("3gears","4gears","5gears")) 
mtcars$am <- factor(mtcars$am,levels=c(0,1),
                    labels=c("Automatic","Manual")) 
mtcars$cyl <- factor(mtcars$cyl,levels=c(4,6,8),
                     labels=c("4cyl","6cyl","8cyl")) 

qplot(wt, mpg, data=mtcars, geom=c("point", "smooth"), 
      method="lm", formula=y~x, color=cyl, 
      main="Regression of MPG on Weight", 
      xlab="Weight", ylab="Miles per Gallon")

qplot(gear, mpg, data=mtcars, geom=c("boxplot", "jitter"), 
      fill=gear, main="Mileage by Gear Number",
      xlab="", ylab="Miles per Gallon")

It perfectly plots in different pages.

Now, I'd like the user to have the choice to plot or not these plots. Therefore, I've changed my script to:

library(ggplot2) 

GENERATE_PLOTS = TRUE

# create factors with value labels 
mtcars$gear <- factor(mtcars$gear,levels=c(3,4,5),
                      labels=c("3gears","4gears","5gears")) 
mtcars$am <- factor(mtcars$am,levels=c(0,1),
                    labels=c("Automatic","Manual")) 
mtcars$cyl <- factor(mtcars$cyl,levels=c(4,6,8),
                     labels=c("4cyl","6cyl","8cyl")) 

if(GENERATE_PLOTS)
{
qplot(wt, mpg, data=mtcars, geom=c("point", "smooth"), 
      method="lm", formula=y~x, color=cyl, 
      main="Regression of MPG on Weight", 
      xlab="Weight", ylab="Miles per Gallon")

qplot(gear, mpg, data=mtcars, geom=c("boxplot", "jitter"), 
      fill=gear, main="Mileage by Gear Number",
      xlab="", ylab="Miles per Gallon")
}

However, when running this, it plots only the last plot...

Can someone enlighten me why this is happening and how can I avoid it? Or if there is better way to deal with these kind of "user preferences" on what he wants the script to do?

Thanks!