C++ random number from a set

Question

Is it possible to print a random number in C++ from a set of numbers with ONE SINGLE statement?

Let's say the set is {2, 5, 22, 55, 332}

I looked up rand() but I doubt it's possible to do in a single statement.

Answer 1

int numbers[] = { 2, 5, 22, 55, 332 };
int length = sizeof(numbers) / sizeof(int);
int randomNumber = numbers[rand() % length];

Answer 2

Pointlessly turning things into a single expression is practically what the ternary operator was invented for (I'm having none of litb's compound-statement trickery):

std::cout << ((rand()%5==0) ? 2 : 
              (rand()%4==0) ? 5 : 
              (rand()%3==0) ? 22 : 
              (rand()%2==0) ? 55 : 
              332
             ) << std::endl;

Please don't rat on me to my code reviewer.

Ah, here we go, a proper uniform distribution (assuming rand() is uniform on its range) in what you could maybe call a "single statement", at a stretch.

It's an iteration-statement, but then so is a for loop with a great big block containing multiple statements. The syntax doesn't distinguish. This actually contains two statements: the whole thing is a statement, and the whole thing excluding the for(...) part is a statement. So probably "a single statement" means a single expression-statement, which this isn't. But anyway:

// weasel #1: #define for brevity. If that's against the rules,
// it can be copy and pasted 7 times below.
#define CHUNK ((((unsigned int)RAND_MAX) + 1) / 5)

// weasel #2: for loop lets me define and use a variable in C++ (not C89)
for (unsigned int n = 5*CHUNK; n >= 5*CHUNK;)
    // weasel #3: sequence point in the ternary operator
    ((n = rand()) < CHUNK) ? std::cout << 2 << "\n" :
             (n < 2*CHUNK) ? std::cout << 5 << "\n" :
             (n < 3*CHUNK) ? std::cout << 22 << "\n" :
             (n < 4*CHUNK) ? std::cout << 55 << "\n" :
             (n < 5*CHUNK) ? std::cout << 332 << "\n" :
             (void)0;
             // weasel #4: retry if we get one of the few biggest values
             // that stop us distributing values evenly between 5 options.

If this is going to be the only code in the entire program, and you don't want it to return the same value every time, then you need to call srand(). Fortunately this can be fitted in. Change the first line to:

for (unsigned int n = (srand((time(0) % UINT_MAX)), 5*CHUNK); n >= 5*CHUNK;)

Now, let us never speak of this day again.