Sorting from a file

heres code I have done so far, I am mostly confused on how to sort the array from the file and store the array.

Code:

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/*
Algorithm:
  1. In the main ( ), open the cars.dat file in the read mode and confirm
        you have properly opened the file.
  2. In the main ( ), read the entire contents of the cars.dat file into the
      inventory array.
  3. In the main ( ), close the cars.dat file
  4. Call function_1( ), which will process the contents of the
        inventory array by sorting the inventory array to place all the cars
        in ascending order according to their price.
  5. Call function_2( ), which will save (write) the sorted inventory
        array to a file named output.dat
  6. Terminate

  ALGORITHM FOR function_1( ):
 1.


*/

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

typedef  struct  cars {
                                          char  make [ 20 ] ;
                                          char  model [ 20 ] ;
                                          char  color  [ 15 ] ;
                                          int  year ;
                                          double price ;
                                      }  cars ;


//Provide the prototype for your PCFs below:
void function_1(cars inventory[], int size);
int main (void)
{
    //Local variables declared... add additional variables as required
    cars  inventory [ 25 ] ;
    int size = 0;
    FILE *input;
    const char *inputfile = "cars.dat";
    //1. Open the cars.dat file in the read mode and confirm
    //    you have properly opened the file.
        input = fopen(inputfile, "r");

    //2. Read the entire contents of the cars.dat file into the
    //    inventory array.
        while ((fscanf(input, "%s%s%s%d%lf",
                  &inventory[size].make, &inventory[size].model,
                  &inventory[size].color, &inventory[size].year,
                  &inventory[size].price
                  ) && (size < 25) ) size++;

    //3. Close the cars.dat file
        fclose(input);

    //4. Call function_1( ), which will process the contents of the
    //    inventory array by sorting the inventory array to place all the cars
    //    in ascending order according to their price.
        function_1(inventory, size);
    //5. Call function_2( ), which will save (write) the sorted inventory
    //    array to a file named output.dat


    //6. Terminate
    return 0 ;
}

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> and confirm // you have properly opened the file.
You don't do this step.

Code:

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        while ((fscanf(input, "%s%s%s%d%lf",
                  &inventory[size].make, &inventory[size].model,
                  &inventory[size].color, &inventory[size].year,
                  &inventory[size].price
                  ) && (size < 25) ) size++;

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You should check the size before doing the input, otherwise you will input over the non existent element 25 only to discover that shouldn't have.
Also, check the fscanf result is specifically 5.

Are you allowed to use this standard function?
qsort, qsort_s - cppreference.com

The essence of sorting is compare and swap.

Code:

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if ( inventory[i].price > inventory[j].price ) {
  cars temp = inventory[i];
  inventory[i] = inventory[j];
  inventory[j] = temp;
}

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You should also turn up your compiler warnings, you have several errors with your code.

Before you worry about sorting the data you should insure that you have read the data correctly (print the array after the read).