Segmentation Fault While Sorting - Malloc

I am reading a file of floating point numbers and then sorting them. When I use my following sort and swap functions with 1 million numbers, I am successfully able to sort the numbers. However, when I try to sort 100 million numbers, I get a segmentation fault. I am not sure why because I am dynamically allocating memory. How would I be able to handle more than 1 million numbers?

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

void swap(float *a, float *b, size_t n) {
    size_t numbytes; 
    size_t sz = sizeof(float); 
    void *temp = NULL; 
    
    numbytes = n * sz; 
    if (numbytes == 0){
        exit(EXIT_FAILURE); 
    }
    temp = malloc(numbytes);
    
    memcpy(temp, a, numbytes);
    memcpy(a,b,numbytes); 
    memcpy(b,temp,numbytes);
    
    free(temp); 
}

void radixSort(float array[], size_t count) {
    int numOfZero = 0; 
    float a[count];
    float *b = a;
    
    for (uint32_t radix=1; radix; radix<<=1) { //unsigned int 32 bit
        uint32_t *arrayToInt = (uint32_t *)array;
        int zeroCount=0;
        int oneCount=0;
        numOfZero=0;
        
        for (int j=0; j < count; ++j)
        numOfZero += !(arrayToInt[j]&radix);
        oneCount=numOfZero;
        
        for (int j=0; j < count; ++j)
        if (arrayToInt[j]&radix){
            b[oneCount]=array[j];
            ++oneCount;
        }
        else{
            b[zeroCount]=array[j];
            ++zeroCount;
        }
        swap(b,array,count);
    }
    if (numOfZero < count){
        memcpy(b+(count-numOfZero), array, numOfZero*sizeof(float));
        
        for (int d=0,j=count-1;j>=numOfZero;j--,d++)
        b[d]=array[j];
        memcpy(array, b, count*sizeof(float));
    }
}
int main(int argc, char *argv[]) {
    int fd; 
    float num; 
    size_t nr; 
    int eleNum = 0; 
    
    fd = open(argv[1], O_RDONLY); 
    
    if (fd == -1){
        perror("Error opening file");
        exit(EXIT_FAILURE);
    }
    
    struct stat st; 
    fstat(fd, &st); 
    off_t size = st.st_size; 
    for (int j = 0; j < size/4; j++){
        eleNum++; 
    } 
    
    float array[eleNum];
    for (int i = 0; i < eleNum; i++){
        nr = read(fd, &num, sizeof(float));
        if (nr == -1){
            perror("Error reading file"); 
            exit(EXIT_FAILURE); 
        }
        array[i] = num; 
    }
    
    radixSort(array, eleNum);
    
    close(fd); 

    return 0; 
}