How can I get an int from stdio in C

Question

I have significant trouble with this     printf   gt      int x   getchar     printf  got the number   d   scanf   d    amp x      Output   gt  1234 got the number  1

User · Answer

The typical way is with scanf   int input value   scanf   d    amp input value     In most cases  however  you want to check whether your attempt at reading input succeeded  scanf returns the number of items it successfully converted  so you typically want to compare the return value against the number of items you expected to read  In this case you re expecting to read one item  so   if  scanf   d    amp input value     1         it succeeded else        it failed   Of course  the same is true of all the scanf family  sscanf  fscanf and so on

User · Answer

The solution is quite simple     you re reading getchar   which gives you the first character in the input buffer  and scanf just parsed it  really don t know why  to an integer  if you just forget the getchar for a second  it will read the full buffer until a newline char   printf   gt      int x  scanf   d    amp x   printf  got the number   d   x     Outputs   gt   prompt expecting input  lets write   1234  Enter  got the number  1234

User · Answer

I m not fully sure that this is what you re looking for  but if your question is how to read an integer using  lt stdio h gt   then the proper syntax is  int myInt  scanf   d    amp myInt     You ll need to do a lot of error-handling to ensure that this works correctly  of course  but this should be a good start   In particular  you ll need to handle the cases where   The stdin file is closed or broken  so you get nothing at all  The user enters something invalid    To check for this  you can capture the return code from scanf like this   int result   scanf   d    amp myInt     If stdin encounters an error while reading  result will be EOF  and you can check for errors like this   int myInt  int result   scanf   d    amp myInt    if  result    EOF               you re not going to get any input            If  on the other hand  the user enters something invalid  like a garbage text string  then you need to read characters out of stdin until you consume all the offending input   You can do this as follows  using the fact that scanf returns 0 if nothing was read   int myInt  int result   scanf   d    amp myInt    if  result    EOF               you re not going to get any input          if  result    0        while  fgetc stdin       n      Read until a newline is found               Hope this helps   EDIT  In response to the more detailed question  here s a more appropriate answer   -   The problem with this code is that when you write  printf  got the number   d   scanf   d    amp x      This is printing the return code from scanf  which is EOF on a stream error  0 if nothing was read  and 1 otherwise   This means that  in particular  if you enter an integer  this will always print 1 because you re printing the status code from scanf  not the number you read   To fix this  change this to  int x  scanf   d    amp x          error checking as above        printf  got the number   d   x     Hope this helps

[c] How can I get an int from stdio in C?

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