Thread: infinite loop kicks in

I can't see what's wrong here, any idea why when I enter q ( which should jump out of the loop ) does the program begin an infinite loop:

Code:

do {
      title (); // a self-defined function for printing text
      printf("\nPlease enter the cost of the item(s)\n");
      printf("(Press q to finish)\n:");
      scanf("%f",&price);
      clrscr();
      cost += price;
      }
      while ( price != 'q' );

You can't store letters in a float variable.

You are scanning a float and then testing it for a character value? That just won't work.
You will have to either:
-scan a 'q' and test it for the value that scanf returns when expecting a float, and then use this value in place of the current 'while' condition,
-use fgets, and test it for q, then transform it with a call to atof, (which is probably better, anyway).

And actually, since in this case, we know noone will enter '0' for a price, we can exploit the fact that atof returns 0 if a char-containing string is passed into it.

Like this:

if( (price = atof( fgets(chPrice, 15, stdin)) == 0 )
break;

cost += price;

>if( (price = atof( fgets(chPrice, 15, stdin)) == 0 )
Be careful doing this, if fgets() returns NULL, then your program will crash.

Well, with file streams, this will probably happen, and often But with keyboard input, I have never had such a problem, EVER. You will always get *at least* a newline. But good eye

I agree Seb, but I never trust a user to do the right thing! They can hit CTRL+D or CTRL+Z on a blank line and it will force a NULL from fgets().

Really? Well, in that case, the bottom line is: "Always perform a sanity check on your fgets() ret val"!!! Thanks for the tip, Hammer.