2D array in C? Process with 2D array

Question

I am writing a program using a 2D array. The user inputs 5 original price values and 5 discount rates for each price. I have the input figured out but I do not understand how to execute the process for a 2D array. I need to figure out the sales price for each original price. My process is:

 amtDiscount = originalPrice * discount;
 salePrice = originalPrice - amtDiscount;

I just don't understand how to do it with the array. I tried doing

amtDiscount = priceDiscount[ROWS] * priceDiscount[COLS];

but when compiling I got this error: subscripted value is neither array nor point

Here is my code:

#include <stdio.h>
#define ROWS 5
#define COLS 5

int main()
 {
    // Declarations
    float priceDiscount[ROWS][COLS];
    float originalPrice = 0.0;
    float discount = 0.0;
    float salePrice = 0.0;
    float amtDiscount = 0.0;
    int i, j = 0;

   //input
   for(i = 0; i < 5; i++)
   {
       printf("Please enter 5 original prices, price %d: ", i+1);
       scanf("%f", &priceDiscount[ROWS]);
   }


   for(j=0; j < 5; j++)
    {
      printf("Please enter the discount rate for each 5 prices, discount
      rate %d: ", j+1);          
      scanf("%f", &priceDiscount[COLS]);
    }

    //Process
   amtDiscount = originalPrice * discount; 
   salePrice = originalPrice - amtDiscount;

   //Output
   printf("Price %%Off Sale");


    /*Test Cases
        Case 1
            Input: $3.50, 25% Output: $3.50, 25%, $2.63
        Case 2
            Input: $5.25, 20% Output: $5.25, 20%, $4.20
        Case 3
            Input: $4.00, 50% Output: $4.00, 50%, $2.00*/

   return 0;

}

Any advice is greatly appreciated! Thanks!

paulsm4 · Accepted Answer · 2015-05-11 03:15:35Z

Actually, I would recommend using an array of struct's:

#define NUM_ITEMS 5

struct {
  float list_price;
  float discount;
} prices;

struct prices current_inventory[NUM_ITEMS];

...
for(i = 0; i < NUM_ITEMS; i++) {
   printf("Please enter 5 original prices, price %d: ", i+1);
   scanf("%f", &current_inventory[i].list_price);
}
for(i = 0; i < NUM_ITEMS; i++) {
   printf("Please enter the discount rate for each 5 prices, discount %d: ", i+1);
   scanf("%f", &current_inventory[i].discount);
}
for(i = 0; i < NUM_ITEMS; i++) {
   printf("sales_price[%d]= %f *f = %f\n",
     current_inventory[i].list_price, current_inventory[i].discount,
     current_inventory[i].list_price * current_inventory[i].discount);
   ...

Untested: but might be a viable alternative for you...

Another variation: you might want to save the sales price (along with other information like "Description" and "quantity" in the record:

struct {
  char description[80;
  int quantity;
  float list_price;
  float discount;
  float sales_price;
} items;
...

R Sahu · Accepted Answer · 2015-05-11 02:57:45Z

You don't need:

float priceDiscount[ROWS][COLS];

to store the original price and the discount. You can use:

float priceDiscount[ROWS][2];

or

float priceDiscount[2][COLS];

If you go with:

float priceDiscount[ROWS][2];

priceDiscount[0][0] can be used to store the original price of the 0-th item and priceDiscount[0][1] can be used to store the discount of the 0-th item.

The lines of code to read the data will be:

for(i = 0; i < 5; i++)
{
   printf("Please enter 5 original prices, price %d: ", i+1);
   scanf("%f", &priceDiscount[i][0]);
}


for(j=0; j < 5; j++)
{
   printf("Please enter the discount rate for each 5 prices, discount
          rate %d: ", j+1);          
      scanf("%f", &priceDiscount[j][1]);
}

Fernando Karpinski · Accepted Answer · 2015-05-11 03:03:20Z

When you create the array, it is correct to use ROWS and COLS. However, if you use such values when processing the array, you will always be accessing position ( 5, 5 ), which, by the way, falls outside the bounds of the array. Any dimension in an array starts its index in 0 and goes on, on increments of 1, until the last index, which equals the size of that dimension - 1. I'm not sure how to process your array, but you could use two nested for statements to accomplish that:

for ( rowCounter = 1 ; rowCounter <= ROWS - 1 ; ++rowCounter )
{
    for ( columnCounter = 1 ; columnCounter <= COLS - 1 ; ++columnCounter )
    {
        //Process element priceDiscount[ rowCounter ][ columnCounter ]
    }
}

In this code, it is assumed that integer variables rowCounter and columnCounter have already been declared. Also, you could view the mechanics of the two nested for statements as: "first, choose a row. Then, process the element of each column in that row. After that, go to the next row, process the element of each column in that row. And so on".

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