C shuffle array

/**
 * Shuffle an array `arr` of length `len`.
 *
 * Having skipped the tutorials on the standard library, I invented this
 * (time-inefficient and space-inefficient) method to solve this problem.
 *
 * Input code removed for the sake of simplicity.
 */

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

void Swap(int *arr, int i, int j) {
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}

int *Zalloc(int len) {
    int *j = (int *) malloc(len*sizeof(int) + 1);
    if (j==NULL) {
        perror("malloc failed\n");
        exit(1);
    }
    return j;
}

void PrintArray(int *arr, int len) {
    for (int i=0; i<len; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

float r, x;    /* static would be better */

int Rand(int *arr, int len) {    /* generate non-repeating PRNG 0<=x<len */
    int rint, rintUnique;
    rint = len * x;
    rintUnique = arr[rint];
    for (int i=rint+1; i<len; i++) {    /* remove already generated */
        arr[i-1] = arr[i];
    }
    x = r * x * (1-x);
    return rintUnique;
}

void ShuffleArray(int *arrIn, int len) {
    r = 3.75;    /* set to other values for different ordering */
    x = 0.5;
    int *arrTemp, *arrRand;
    arrTemp = Zalloc(len);
    arrRand = Zalloc(len);
    for (int i=0; i<len; i++) {
        arrTemp[i] = i;
    }

    int rint;
    int lenTemp = len;
    for (int i=0; i<len; i++) {
        rint = Rand(arrTemp, lenTemp);
        arrRand[i] = rint;
        //printf("rint is %d\n", rint);
        lenTemp--;
    }

    int lenHalf = len / 2;
    for (int i=0; i<lenHalf; i++) {
        Swap(arrIn, arrRand[i], arrRand[lenHalf+i]);
        //printf("swapped elements %d and %d\n", arrRand[i], arrRand[lenHalf+i]);
    }
    free(arrTemp);
    free(arrRand);
}

int main() {
    int array[] = {2,3,5,7,11,13,17,19,23,29,31};
    int len = sizeof(array) / sizeof(int);

    printf("original: ");
    PrintArray(array, len);
    if (len<10) {
        printf("\nArray is too short. Exiting\n");
    } else {
        ShuffleArray(array, len);
        printf("shuffled: ");
        PrintArray(array, len);
    }
    return 0;
}