This C code performs several tasks, depending on which `main`...

August 22, 2025 at 04:41 PM

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

void init_random(int arr[], int length) {
    srand(time(NULL));
    for(int i=0; i<length; i++){
        arr[i]=rand() % 65536;
    }
}

int population(int n) {
    int con=0;
    while(n!=0){
        if(n%2==1){
            n=(n/2)+ 1;
            con+=1;
        }else
            n=n/2;
    }
    return con;
}
/*
// ordina gli elementi di arr in ordine non decrescente per popolazione
void sort_by_population(int arr[], int length) {
  // COMPLETARE
}

int main(void) {
  int length;

  do {
    printf("Inserisci la lunghezza dell'array, non negativa: ");
    scanf("%i", &length);
  }
  while (length < 0);

  int elements[length];
  init_random(elements, length);
  sort_by_population(elements, length);

  for (int pos = 0; pos < length; pos++)
    printf("%i (popolazione %i)\n", elements[pos], population(elements[pos]));

  return 0;
}
*/
int main(void){
    int entry;
    printf("Prego inserire il nuemro : ");
    scanf("%i", &entry);
    int c=population(entry);
    printf("%i", population(5));
    printf("\n%i", 5/2);
    return 0;
}

This C code performs several tasks, depending on which main function is active. The first main function (inside the commented block) aims to work with arrays of random integers, while the second main function (at the bottom) handles population-related calculations for a single number. Let's break it down in detail:

Key Components

init_random Function:
- This function initializes an array (arr) of integers with random values between 0 and 65535 (i.e., within the range of 16-bit integers).
- The function seeds the random number generator (srand(time(NULL))) with the current time, ensuring a different sequence of random numbers each time the program is executed.
population Function:
- Computes a specific "population" measure for a given integer n.
- The process involves repeatedly checking whether n is odd or even:
  - If n is odd (n % 2 == 1), increment a counter (con) and set n to (n / 2) + 1.
  - If n is even, simply divide n by 2.
- The function continues until n is reduced to 0, returning the final count stored in con.
Commented main Function:
- Prompts the user to input the length of an array (must be non-negative).
- Allocates an array of the specified length and initializes it with random values using init_random.
- A placeholder function, sort_by_population, is included but not yet implemented. Its intended purpose is to sort array elements in non-decreasing order based on the "population" of each element (using the population function).
- Prints the array values alongside their "population" values.
Active main Function:
- Prompts the user to input a single integer, entry.
- Computes the "population" of the entered number using the population function.
- Demonstrates the functionality of integer division in C by returning both:
  - population(5)
  - The integer division 5 / 2, which evaluates to 2.

What Happens When You Run This Code?

The active main function does the following:

Asks the user to enter an integer (entry).
Calculates the "population" of entry (though the result is not printed).
Prints:
- The population of 5 (population(5)).
- The result of 5 / 2 (integer division).

For example, if the user enters entry = 7:

The code prints:
- 3 (since population(5) is 3).
- 2 (integer result of 5 / 2).

If you activate the commented main and implement the sort_by_population function, the program becomes an array-based tool that sorts integers by their "population" value, but this feature is incomplete as no sorting logic is provided.

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