Help with Probabilities & C++ Programming

[Tenshou]

I am not sure how to assign probabilities to variables do you think you guys will be able to help me?

 

[Adyssa]

Can you be more specific? Do you know how to assign probabilities on paper? If so, it shouldn't be too hard to translate your paperwork into source code.

 

[Tenshou]

No, I mean how do you give a variable a probability, for example, in a conditional statement you will printf(hello world) when the probablity is 1/3 or you will printf(Good Day!) if the probability is 1/3 or printf(Good Bye) if the probability is 1/3. What I mean is how will I get a conditional statement to run as if they were probablities... would I just conjoin it with if, else ,when statements?

 

[Adyssa]

I don't use C++, but you can generate a random number and then decide on a course of action depending on the result. For example:

#include <stdlib.h> // C standard library
float num = rand() % 9; // this is the C rand function, and your number will be between 0-8

if (num < 3)
{
  // do something
}
else if (num >= 3 && num <= 6)
{
  // do something else
}
else // implication num > 6 && num <= 8
{
  // do something else
}

Your random number will be in one of the 3 ranges with 1/3 probability, although it's worth noting that rand() is a pseudo-random number generator, but it's probably fine for your purposes.

 

[Tenshou]

Thank you! How would you make this loop keep going without terminating?

 

[jtbell]

Do you know how to make a loop that does terminate? Simply use a loop condition that never becomes 'false'.

 

[Mark44]

I don't use C++, but you can generate a random number and then decide on a course of action depending on the result. For example:

#include <stdlib.h> // C standard library
float num = rand() % 9; // this is the C rand function, and your number will be between 0-8

if (num < 3)
{
  // do something
}
else if (num >= 3 && num <= 6)
{
  // do something else
}
else // implication num > 6 && num <= 8
{
  // do something else
}

Your random number will be in one of the 3 ranges with 1/3 probability, although it's worth noting that rand() is a pseudo-random number generator, but it's probably fine for your purposes.

Thank you! How would you make this loop keep going without terminating?

What Adyssa wrote is NOT a loop; it's an if...else block. To make this a loop, you would need to embed the if-else block in a loop of some kind.

 

[Tenshou]

when I said "when statement" I meant to say while sorry >.< so I would make a bool variable and have it always true while the conditional is looping or something of that fashion?

 

[AlephZero]

so I would make a bool variable and have it always true while the conditional is looping or something of that fashion?

Correct, but you don't need to use a variable. This is usually written as

while (true) {
// do something
}

The "do something" code probably needs to contain a "break" statement somewhere, unless you really want the program to run for ever!

 

[Mark44]

You could do something like this:

while (1)
{
   Get a random number (in the range 0 .. RAND_MAX)
   Turn it into a probability by dividing by RAND_MAX
   if (prob < .3333)
   {
      do something
   }
   else if (prob < .6666)
   {
      do something else
   }
   else 
   {
      do the third thing
   }
}