User Input check

[emryoz]

Hi,
I need a hint on how to make sure the user is entering a positive integer (no strings, no characters in between numbers, no negative numbers). The method I am trying to use is "atoi" conversion and the problem is it messes up when I try to enter zero although zero is an acceptable number. Here is my code;

int confirm, flag, down, up;
char number_of_entities[200], answer[100];

while(confirm)
{
printf("Input the number of entities> "
scanf("%s", &number_of_entities);
printf("\n"
flag = 1;
while(flag)
{
down = (int)(floor(atof(number_of_entities)));
up = (int)(ceil(atof(number_of_entities)));

if(atoi(number_of_entities)>MAX_NUMBER || atoi(number_of_entities)<0)
{
printf(&quot;Please enter an appropriate number!!!\n&quot;
scanf(&quot;%s&quot;, &number_of_entities);
}

else
{
if(up == down)
flag = 0;
else
{
printf(&quot;Please enter an appropriate number!!!\n&quot;
scanf(&quot;%s&quot;, &number_of_entities);
}
}
}

printf(&quot;Number of entities you entered is> %d\n&quot;, atoi(number_of_entities));
printf(&quot;Is this correct?(y/n)\n&quot;
scanf(&quot;%s&quot;, &answer);
if(answer[0] == 'y' || answer[0] == 'Y')
{
confirm = 0;
}
if(answer[0] == 'n' || answer[0] == 'N')
{
confirm = 1;
}
}

Thanx

 

[emryoz]

I didn't get any response yet. C'mon folks I know you can tackle this problem.

 

[LiquidBinary]

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int verifyInt( char* s )
{
char c;
int i;

i=0;
if( s[0]=='0' && s[1]=='\0' )
return( 1 );
if( s[0]=='0' && s[1]!='\0' )
return( 0 );

while( 1 )
{
c=s[i++];
if( c=='\0' )
break;

if( !isdigit( c ) )
return( 0 );
}

return( 1 );
}

int main( void )
{
char sInput[20];

printf( &quot;Enter a positive int: &quot; );
fgets( sInput,sizeof( sInput ),stdin );
*( strrchr( sInput,'\n' ) )='\0';

if( !verifyInt( sInput ) )
printf( &quot;Please enter a valid positive int.\n&quot; );
else
printf( &quot;You entered: %d\n&quot;,atoi( sInput ) );

return( 0 );
} Mike L.G.
mlg400@linuxmail.org

 

[emryoz]

Thank you very much Mike. It works great. I appreciate it.

 

[rbobbitt]

Something like this should work (untested):

#include <errno.h>
#include <limits.h>
#include <stdlib.h>

/* Returns 1 if s can be converted
* to a positive integer, 0 otherwise */
int verify(const char *s,int base)
{
char *endptr
(void)strtoul(s,&endptr,base);
return errno!=ERANGE && !*endptr;
}
Russ
bobbitts@hotmail.com

http://home.earthlink.net/~bobbitts