Programming

#include "stdio.h"
#include "stdlib.h"

#define VSIZE  256/8            // vector size in bytes
void mark( unsigned char *vector, unsigned char byte )
{
    int idx;
    int mask;

    idx = byte / 8;
    mask = 1 << (byte % 8);

    vector[idx] |= mask;
}

int check( unsigned char *vector, unsigned char byte )
{
    int idx;
    int mask;

    idx = byte / 8;
    mask = 1 << (byte % 8);

    return vector[idx] & mask;
}

int main( int argc, char **argv )
{
    unsigned int    value;
    unsigned char vector[VSIZE];

    printf( "enter non-number or ctl-D to quit\n" );
    for( ; ; )
    {
        printf( "enter a number (0-255): " );
        if( scanf( "%u", &value ) <= 0 )        // read value converting it to unsigned
        {
            printf( "\n" );
            exit( 0 );
        }
        if( value < 256 )
        {
            printf( "the value %u has %sbeen entered before\n", value, check( vector, value ) ? "" : "not " );
            mark( vector, value );
        }
        else
            printf( "%d is out of range for a byte\n", value );
    }

    return 0;
}