While loop in C which genrates random numbers running for infinity-CodePudding

I want to make a program, which generates 2 random coordinates and then it tests if the place in the 2D array I made before is empty (the value in the array is 0). If true, it places value 2 to that coordinates, else it should keep looking for such place. The issue is that it is running for infinity in some cases.

Here is the array I made:

int array[4][4] =
{
    {0,0,0,0},
    {0,0,0,0},
    {0,0,0,0},
    {0,0,0,0}
};

Here is the rest of the code:

srand(time(NULL));
int ranadom_num[2] = { rand() % 4, rand() % 4 };
while (array[ranadom_num[0]][ranadom_num[1]] != 0)
{
    int ranadom_num[2] = { rand() % 4, rand() % 4 };
}
array[ranadom_num[0]][ranadom_num[1]] = 2;

Any help? :)

CodePudding user response：

There are two variables in given piece of code,

int ranadom_num[2] = { rand() % 4, rand() % 4 }; //here 1

while (array[ranadom_num[0]][ranadom_num[1]] != 0)
{
    int ranadom_num[2] = { rand() % 4, rand() % 4 }; //here 2
}

so, random_num picked at 1 is not changed inside the loop and random_num at 2 is of no use as it is unused in the given scope (i.e inside loop).

Find the updated code here,

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

int
main ()
{
  int array[4][4] = {
    {1, 2, 3, 4},
    {5, 6, 7, 8},
    {9, 10, 11, 12},
    {0, 0, 0, 0}
  };

  srand (time (NULL));
  int ranadom_num[2] = { rand () % 4, rand () % 4 };
  while (array[ranadom_num[0]][ranadom_num[1]] != 0)
    {
      printf ("%d ", array[ranadom_num[0]][ranadom_num[1]]);
      ranadom_num[0] = rand () % 4;
      ranadom_num[1] = rand () % 4;
    }
  array[ranadom_num[0]][ranadom_num[1]] = 2;

  return 0;
}

You also need to take care of values inside array. At lease one element must be zero to terminate the loop else it will be infinite loop.

CodePudding user response：

You're redeclaring ranadom_num in the loop and you're not setting the value in the array until after the loop completes, which is why you're getting the infinite loop.

srand(time(NULL));
int ranadom_num[2] = { rand() % 4, rand() % 4 };
while (array[ranadom_num[0]][ranadom_num[1]] != 0)
{
    //now there's a chance that the array will have a 2 in it
    array[ranadom_num[0]][ranadom_num[1]] = 2; 
    ranadom_num[0] = rand() % 4;
    ranadom_num[1] = rand() % 4;
}