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/*
* Choose.c - A program to calculate and print the value of
* the choose function C(n, r).
* This program is the model solution to Quiz #3 (take home).
* It also illustrates a fancy input technique.
*
* Written by Wayne Pollock, 2001 Tampa Florida USA.
*/
#include
#define OK 1
/* P R O T O T Y P E S */
int check ( int n, int r ); /* Checks if r < n */
unsigned long choose ( int n, int r ); /* Computes C(n,r) */
unsigned long fact ( unsigned long num ); /* Computes num! */
int main ( void )
{
int n, r;
char line[BUFSIZ], junk[BUFSIZ];
fprintf( stderr, "Enter positive integers n and r: " );
if ( fgets( line, sizeof(line), stdin ) == NULL )
{ fprintf( stderr, "*** ERROR! End Of File encountered!\a\n" );
return -1;
}
if ( sscanf( line, "%i %i %s", &n, &r, junk ) != 2 )
{ fprintf(stderr, "*** ERROR! You must enter exactly 2 numbers,"
" separated by white space!\a\n" );
return -2;
}
if ( check( n, r ) != OK )
return -3;
printf( "C(%i,%i) = %lu.\n", n, r, choose( n, r ) );
return 0;
}
int check ( int n, int r )
{
if ( n < 0 || r < 0 )
{ fprintf( stderr, "*** ERROR! Numbers must be POSITIVE!\a\n" );
return !OK;
}
if ( r > n )
{ fprintf( stderr, "*** ERROR! n must be as large or larger "
"than r!\a\n" );
return !OK;
}
return OK;
}
unsigned long fact ( unsigned long num )
{
unsigned long result;
for ( result = 1; num; --num )
result *= num;
return result;
}
unsigned long choose ( int n, int r )
{
return ( fact(n) / fact(r) / fact(n-r) ); /* Note: A/(B*C) = A/B/C */
}
/*
============================Output of Choose.c============================
Enter positive integers n and r: 5 2
C(5,2) = 10.
*/