#switch
centre <- function(x, type) {
  switch(type,
        mean = mean(x),
        median = median(x),
        trimmed = mean(x, trim = .1))
}


#ifelse

example.ifelse=function(x){

		z=ifelse(x >= 0, sqrt(x), NA)

		return(z)
		}

#break
example.break=function(x){

	for(i in 1:x){

		print(i)
	
		if(i>5){
			break
				
			}
		}
	}

example.break2=function(A,B){

	for (i in 1:A){

		for (j in 1:B){
	
			if (j==3) {
		
				break
			
				}
			
			else {
		
				cat (i,j,"\n")
				}
		}

	}
	
}	


example.next=function(A,B){

	for (i in 1:A){

		for (j in 1:B){
	
			if (j==3) {
		
				next
			
				}
			
			else {
		
				cat (i,j,"\n")
			
				}
		}

	}
}



###
#stop

# write a function which stops and gives a warning when argument is smaller then 0. 


Sqrt=function(x){

		if(x<0) stop("Argument should be >= 0")
		
		else sqrt(x)
		
		}
		}