Thread: do while loop and modulus question - lotto picker

reference: C ALL IN ONE DESK REFERENCE pg 40.

The code below creates random numbers and displays them. It keeps a track of the numbers generated so they are not repeated. Similar to the lotto

The trouble I'm having is with the do while loop specifically while(numbers[ball]). Does it mean to say while numbers[ball]=1 it should repeat ?

Also, lets say a random number 20 is created. What does ball=rand()%RANGE be equal to? 0.4?

Code:

#include <stdio.h> 
#include "stdafx.h" 
#include <stdlib.h> 
#include <time.h> 

#define RANGE 50 
#define BALLS 6 
int main() 
{ 
   int numbers[RANGE]; 
   int c,ball; 

   puts("LOTTO PICKER\n"); 

   srand((unsigned)time(NULL)); 

   //initialize the array 
   for(c=0;c<RANGE;c++) 
      numbers[c]=0; //all 50 elements are initialized to 0 

   printf("Press Enter to pick this week's numbers:"); 
   getchar(); 

   //drawing numbers 
   puts("Here they come"); 

   for (c=0;c<BALLS;c++) 
   { 
      do 
      { 
      ball=rand()%RANGE; 
      }while (numbers[ball]); 
       
   numbers[ball]=1; 

   printf("%2d ",ball+1); 
   } 
    

getchar(); 
getchar(); 
}

In C/C++ boolean assignments are basically broken down into this

Code:

if( a ) is really saying if ( a != 0)

and

Code:

 if ( !a ) is really saying if ( a== 0 )

The do-while loop's condition is verifying that numbers[ball] is nonzero.

So the loop will continue until numbers[ball] (a random member in the array) is zero.
Then it apparently assigns a value of 1 to it. (probably boolean for chosen)
spits out the index of that random number+1

so in pseudo
I have fifty indexes, so long as none of them have been picked before print the value of this random index