Thread: if statements using strings as the condition

1) void main is bad. Search the FAQ and the board to find out why.
2) You can't compare the values of two strings using the == operator.
3) To do what you need, #include <string.h> and change or if statement to:

Code:

if( strcmp(strBoolean, "Y") == 0 || strcmp(strBoolean, "y")== 0)

4) An even better way for what you want to do is instead of a string use a single character and use getchar()
5) fscanf is generally better for user input then scanf.

edit: note the " " instead of ' ' around the Y. ' ' denotes a single character whlie " " denotes a string.

getchar() gets a single character from the input stream and assigns it to the variable. So you can do:

Code:

#include <stdio.h>
int main (void)
{
  int ch;

  ch=getchar();

  if (ch == 'y' || ch == 'Y')
  /* rest of code */
}

The reason for int ch instead of char ch is because thats what getchar returns. C treats chars at short integers so the above comparison is legal.

Actually I was wrong to use fscanf to get the input info. I meant fgets. This is a function to get a string from a stream. scanf has a problem if you input "yes" and also will leave the newline (think the character that is sent when you press enter) in the buffer. fgets will only get the number of characters allowed by the size and will also capture the newline character if there is room.

Way to use it would be like this (for your program)

Code:

fgets ( strBoolean, sizeof(strBoolean), stdin)

Do a search and you'll be able to find a lot more information about it, I think its in the FAQ also. Look for why gets is bad.

For trang:
The way you're using scanf is dangerous. If the input is more than 1 character long, then you'll overwrite the array into which you're reading data. You need to specify the length of the string argument (%s) that you're asking scanf to read. In this case, 1 character.

Also, you need to check the value returned by scanf. There's no guarentee that it has read anything meaningful. Try:

Code:

int status=0;

do {
  /* print message asking for input */
  status=scanf("%1s",strBoolean);
  if (status==EOF) {
    /* error or end of file encountered - report the error and die */
  } else if (status!=1) {
     /* scanf didn't match anything sensible, the user probably typed nonsense. Say so */
  }
} while (status!=1);

As Thantos has said already:
1) don't use voide main, or even void main.
2) do use strcmp to compare strings, not == ...

For explaination, a==b compares the values of a and b. In the case of strings, a and b are typically either pointers to char or array identifiers which 'decay' in that context to pointers to the first element (again, a pointer to char). For strings, these pointers point to the start of an array of characters terminated by a '\0' character. a==b then, would compare the value of the /pointers/ not the /contents/ of the strings. strcmp() on the other hand, compares the strings the pointers point to and returns 0 if the strings are the same.

3) consider using getchar instead of scanf

Getchar will read a single character from the standard input stream (stdin). The value returned is either EOF (when EOF or an error occurs IIRC) or the value of a character.

The downside is that most C implimentations have buffered input on stdin. The user would typically be able to type a whole load of things - more than one character - and then enter. At that point, the C implimentation will handle your getchar and retrieve the first character. The rest of the characters entered by the user in the buffer will stay there until you read them. In that case, get your character and process it. Then, clear the input buffer by reading it in character by character until EOF occurs (there's no more characters) or a newline '\n' character is encountered.


<snipped - query about fscanf, which thantos has clarified whilst I wasn't looking>

Ian Woods