This program is only supposed to accept alpha characters ie ABCD. But it is accepting alphanumeric input such as ABCD9. What am I dong wrong?
Code:void A_getOriginalString() { if (!(isalpha(*originalString))) /* Why does work for 5554 but not for ABCD9? */ { puts("Letters only please. Try again.\n"); fflush(stdin); gets(originalString); } }
Test one character at a time.
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
Duh!! I Thanks!Originally Posted by MK27
This worked...
Code:void A_getOriginalString() { int i; int length = strlen(originalString); for (i = 0; i < length; ++i) { originalString[i]; } if (!(isalpha(originalString[i++]))) { puts("Letters only please. Try again.\n"); fflush(stdin); gets(originalString); } }
Oops! Perhaps this doesn't work. Now it's not accepting any string as valid input.
Okay, now I think I got it for realz....
Code:int i; int length = strlen(originalString); for (i = 0; i < length; ++i) { originalString[i]; if (!(isalpha(originalString[i]))) { puts("Letters only please. Try again.\n"); fflush(stdin); gets(originalString); } }
Okay maybe I had it for fakes. I think it should beCode:length - 1
Nope. It's because you are pre-incrementing (as opposed to post-incrementing) i:Okay maybe I had it for fakes. I think it should be
Code:length - 1
Use i++. And the line in red is meaningless/superfluous.
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
Ahh... Very cool! Thanks!
This results in undefined behaviour:
This makes you vulnerable to a buffer overflow:Code:fflush(stdin);
I suggest that you write isalpha for a string, e.g.,Code:gets(originalString);
Now, in the loop where you request for the user to enter the string, read in the input using something safer like fgets(), then use isalphaString() to check if the input is correct. If it is, end the loop, otherwise print the error message and request for user input again.Code:int isalphaString(const char *str) { for (; *str != '\0'; ++str) { if (!isalpha(*str)) { return 0; } } return 1; }
If you do use fgets(), then note that it places the newline in the string unless the string read is of the maximum length. Consequently, it may be useful to write a function to simplify the process of removing that newline, then replace the fgets() call with it, e.g.,
Code:char *getLine(char *str, size_t size, FILE *fp) { if ((str = fgets(str, size, fp))) { char *new_line = strchr(str, '\n'); if (new_line) { *new_line = '\0'; } } return str; }
Last edited by laserlight; 02-15-2009 at 12:24 AM.
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