array_of_integers.c

/*

    array_of_integers.c

    Task from:
    https://www.facebook.com/photo/?fbid=279404964292467&set=gm.1550830281966942


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>
#include <math.h>

// Function to print array, n is number of elements in array arr[]
// text[] describes the shown array arr[]
void ShowArray(char text[],int arr[],int n)
{
    int i;

    printf("\n n = %d ", n);
    printf("%s",text);
    for(i=0;i<n;i++)
        printf("%5d", arr[i]);

    printf("\n");
}

// Function to swap two integers, with pointers
void swap(int *xp, int *yp)
{
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
}

// function bubbleSort to sort the array in descending order
void bubbleSortDescending(int arr[], int n)
{
    int i, j;

    for (i = 0; i < n-1; i++)
        for (j = 0; j < n-i-1; j++)     // Last i elements are already in place
            if (arr[j] < arr[j+1])      // arr[j] > arr[j+1] for ascending order
                swap(&arr[j], &arr[j+1]);
}

void removeEvenIntegers(int arr[], int *n)
{
    int i,k=0;

    for(i=0;i<*n;i++)
        if(arr[i]%2==0)
            ;                   // do nothing
        else
            arr[k++]=arr[i];

    *n=k;
}

// reverse array of integers
void reverse_array( int arr[], int n )
{
    int i, j, mem_int;          // n is number of integers in arr[]

    // reverse array
    for( i=0,j=n-1; i<n/2; i++,j-- )
    {
        mem_int    = arr[i];
        arr[i]   = arr[j];
        arr[j] = mem_int;
    }
}

// Returns 1 if num is prime, otherwise returns 0.
int is_prime(int num){
    int i;
    float sq = sqrt(num);
    if( num < 2 )
        return 0;
    for(i=2; i<=sq; i++)    // it is enough to go to the root of the number !
        if(num % i == 0)    // if the number is divisible by i,
            return 0;       // it is not prime number
    return 1;
}

int removeNotPrimeIntegers(int arr[], int *n)
{
    int i,k=0;

    for(i=0;i<*n;i++)
        if( is_prime(arr[i]) )
            arr[k++]=arr[i];
        else
            ;               // do nothing

    *n=k;
}

// Swap the last number of the arr with the first number of arr.
void swap_last_and_first_number_of_array(int arr[], int n)
{
    int temp;

    temp=arr[0];
    arr[0]=arr[n-1];
    arr[n-1]=temp;
}


int main(void){
    int arr[]={5,34,7,56,32,1,0,12,8,76,78,23,2,56,28,56,23,65,13,34,45,3,76,25,15,32,76,34,30,29};
    int i, n=sizeof(arr)/sizeof(int);

//  n=30;
//  printf("\n Enter %d integers for array \n", n);
//  for(i=0;i<n;i++)
//      scanf("%d", &arr[i]);
//  n=i;
    ShowArray("\n Array is :\n", arr, n);

    bubbleSortDescending(arr,n);
    ShowArray("\n Descending sorted array is :\n", arr, n);

    removeEvenIntegers(arr,&n);
    ShowArray("\n Array without even integers is : \n", arr, n);

    reverse_array(arr,n);
    ShowArray("\n Reversed array is : \n", arr, n);

    removeNotPrimeIntegers(arr,&n);
    ShowArray("\n Array without not prime integers is : \n", arr, n);

    swap_last_and_first_number_of_array(arr,n);
    ShowArray("\n Array after swapping first and last number is : \n", arr, n);

    printf("\n\n");
    return 0;
} // main()