wrong name of input file and goto like function

Dear all,

I have a question and need your help please.
I have the following code which is asking user to enter the name of their file.

define<- function()
?{
?readline("enter the name of your file: ")
?}

df=read.table(define(),fill=T,sep="\t",colClasses = "character")

Now I want if user will input wrong name of file the code should not end and it should show a message-

if()
{
?print("wrong name of the file Please enter again ")

?}

now I want to ask what should be the condition of if so that if user will input wrong file name it will show this message and then i want to use something like goto so that it should again start with the code which is before if condition-

df=read.table(define(),fill=T,sep="\t",colClasses = "character")




so the code should be-

define<- function(x)
?{
?readline("enter the name of your file: ")
?}

df=read.table(define(),fill=T,sep="\t",colClasses = "character") ? ? ? ? ? ##starline


if(## some condition here)
{
?print("wrong name of the file Please enter again ")
## some goto function so that it should goto (starline)
?}







Thanking you,
Warm Regards
Vikas Bansal
Msc Bioinformatics
Kings College London

Thanks for you reply.I have seen it and I got that we can use this goto function in the form of double loop.

like-

for(j in 1:10)
{
df=read.table(define(),fill=T,sep="\t",colClasses = "character")
if()
{
print("wrong name of the file Please enter again ")}
else{
break()
}
}

but i did not find what should i condition should i give in if statement because when the user will type the wrong name of the file,my code does not execute and just showing the eroor

could not find such file

Can you please tell me what condition i should write so that my code should not stop even if user writes wrong name of input file?

Thanking you,
Warm Regards
Vikas Bansal
Msc Bioinformatics
Kings College London

Dear all,

I have a question and need your help please.
I have the following code which is asking user to enter the name of their file.

define<- function() 
{ 
readline("enter the name of your file: ") 
} 

df=read.table(define(),fill=T,sep="\t",colClasses = "character")

Now I want if user will input wrong name of file the code should not end and it should show a message-

if()
{
print("wrong name of the file Please enter again ")

}

now I want to ask what should be the condition of if so that if user will input wrong file name it will show this message and then i want to use something like goto so that it should again start with the code which is before if condition-

df=read.table(define(),fill=T,sep="\t",colClasses = "character")




so the code should be-

define<- function(x) 
{ 
readline("enter the name of your file: ") 
} 

df=read.table(define(),fill=T,sep="\t",colClasses = "character")           ##starline


if(## some condition here)
{
print("wrong name of the file Please enter again ")
## some goto function so that it should goto (starline)
}







Thanking you,
Warm Regards
Vikas Bansal
Msc Bioinformatics
Kings College London