Algorithm for generating weighed random numbers in objective c

-(int) randomIndexByWeights:( NSArray* )weights

{

    // add weights

    int weightsTotal = 0;

    

    for( int i = 0; i < [weights count]; i++ )

    {

        weightsTotal+= [[weights objectAtIndex: i] intValue];

        

    }

    float randomNum = ((float)rand() / RAND_MAX) * 1;

    int rand =(int)(randomNum * weightsTotal);

    // step through array to find where that would be

    weightsTotal = 0;

    for( int x = 0; x < [weights count]; x++ )

    {

        

        weightsTotal+= [[weights objectAtIndex: x] intValue];

        

        if( weightsTotal >= rand)

        {

            return x;

        }

    }

    // if random num is exactly = weightsTotal

    return [weights count] - 1;

}

    NSArray *weights=@[@75,@20,@5];

    NSArray *typeArray=@[@"s",@"m",@"b"];

    NSString *type;

  

      for(int i=0;i<100;i++)

    {

        type = typeArray[ [self randomIndexByWeights:weights]  ];

         //75 time is string s displayed

        //70 time is string m displayed

        //5 time is string b displayed

     }