Writing a function that will overwrite values in main function array

Question

I'm given a problem in which the main function is already provided and I need to create a function that would calculated whatever is asked. I'm having problems trying to figure out how to overwrite the array in the main function with the new values I obtained from the function I created. So far, the end result is that it just prints out whatever is from the original array.

#include "stdafx.h"
//Windows Visual studio seems to want me to add this in order for it to work
#include <iostream>
#include <fstream>
#include <string>
using namespace std;


void change_price(float price[], float percent_change){

    for (int j = 0; j < 8; j++){
    (price[j] * (100 + percent_change)) / 100 ;
   }    
}


/*
This program inputs an array of item prices on sale
There is a 25% discount and the NY sales tax 8.875 is computed on the     reduced price
It then prints the resulting prices
*/
int main(){
    float prices[] = { 10, 27, 83, 15, 39, 120, 87, 20 };
    change_price(prices, -25.0);
    change_price(prices, 8.875);
    cout << "final prices\n";
    for (int i = 0; i < 8; i++)
        cout << prices[i] << endl;

}

Thanks for the quick response! I get the gist of what you're saying in terms of how the changes go away after the change_price finishes. I'm not 100% sure what you mean in terms of passing the address of price however. Just to reiterate, I'm not allowed to make any changes to the main function. I can only play around with the change_price function. Thanks again. — trungnt
– trungnt, Commented Apr 20, 2015 at 7:41

MikeMB · Accepted Answer · 2015-04-20 08:10:02Z

2

The reason you see no change is, because you don't assign any new values to your array in your function. Try something like:

price[j]=(price[j] * (100 + percent_change)) / 100 ;

in your loop.

EDIT:

Some advice from my part: If you ever have to write code like this (in the main function) yourself, use std::vector or std::array. Unfortunaltey / luckyly, they are no drop-in-replacements for c-style arrays, but in addition to some other advantages, they will eliminate any confusion about pass-by-reference or pass-by-value

edited Apr 20, 2015 at 8:10

answered Apr 20, 2015 at 7:45

MikeMB

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1 Comment

trungnt Over a year ago

Ah, there we go. Works exactly the way I want it to now! Thanks so much for the help. Shamefully, I was having so much trouble with something so simple. Much appreciated.

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