c integer checking

[delta770]

hi

i have a program where the user inputs an int. i wanna check if the int is valid, ie, no other characters besides numbers. i'm trying to get one character at a time from the int and check if 'isdigit()', but i'm not sure how to do this right or if there are alternatives...

any help is appreciated.
thank you
--770

[Technocrat]

Here is some code that I made. I know there is a function some where, maybe the STL that will do this as well, but I always use mine.

#define _ISDIGIT 0x10

inline bool IsDigit(char *buf){return((*buf & _ISDIGIT) ? 1 : (*buf =='.'));} 

[delta770]

i'm new to c, so is there anything simple i could use? i think isdigit is in ctype.h, but it only accepts one digit at a time. how do i get one digit at a time from a big integer.

also i don't understand your code, so i'm not sure how i can implemet it into mine..

thanx though

--770

[jim mcnamara]

You have to read string characters, then check if they are valid, then convert to int.

#include <ctype.h>
char answer[10];
char *buf;

int number=0;
memset(answer,0x00,sizeof(answer));

while(1){
      printf("Enter a number: ");
      gets(answer);
      if(strlen(answer)){
      /* this next line reads thru the string looking only for digits */
        for(buf=answer;*buf && IsDigit(*buf);buf++);
        if (!*buf) break; /* if we read to the end of the stringit was okay */
      }
      printf("\nInvalid response. Please use numbers only\n");
}
number=atoi(answer);

[CornedBee]

not
gets(answer);
but
fgets(stdin, answer, 9);

or you risk buffer overflows.