Why a i getting this message after i compile my program

c:\program files (x86)\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\..\..\..\libmingw32.a(main.o):main.c|| undefined reference to `WinMain@16'|

```
/*
* p2.cpp
*
* Created on: Oct 7, 2010
* Author: saturner
*/
#include "p2.h"
#include <iomanip>
#include <string>
using namespace std;
int main ();
/*
* Converts an amount measured in cups to milliliters.
* 1 cup = 236.518538 milliliter
*
* cups - amount measured in cups
*
* returns amount in milliliters
*/
double convertCupstoMilliliter(double cups)
{
//modify -1 below to be your new calculated value.
return cups * 236.518538;
}
/*
* Returns the percent change from the original to the desired servings.
* The percent is expressed as a decimal. i.e.:
* 1 = 100%
* 0.5 = 50%
* 1.5 = 150%
* If either of the serving values is 0, a value of 1 serving is assumed.
*
* To calculate the number of servings, the following formula is used:
*
* Desired Servings =
* | Desired Servings / Original Servings | - 0.1 *
* (1 - | Desired Servings / Original Servings | )
*
* where | x | is the absolute value of x
*
* original - number of servings the recipe was designed for
* desired - the number of servings wanted
*
* returns the % change that should apply to all of the ingredients.
*/
double changeServings(int original, int desired)
{
//stops any division by 0
if (original == 0)
{
original = 1;
}
if (desired == 0)
{
desired = 1;
}
//end check
double rate = desired / (double)original;
if(rate < 0)
rate = -rate;
//modify -1 below to be your new calculated value.
return (rate - 0.1 * (1 - rate));
}
//given an amt and a percent change, find the new amt
/*
* Given the amount of a ingredient and the % change due to the
* change in the number of servings, calculates the new amount.
*
* amt - original amount from the recipe
* changeInServings - % to change amt
*
* returns corrected amount
*/
double convertAmtByServings(double amt, double changeInServings)
{
//modify -1 below to be your new calculated value.
return amt * (changeInServings);
}
//out the ingredient, and amounts
//35, 12.2c, 12.2ml
/* Outputs a single ingredient and its amounts in both cup and milliliter units.
*
* Data should be formatted to the following constraints:
*
* Value Width Decimal places Alignment
* --------------------------------------------------
* ingredient 35 - left
* amtInCups 12 2 right
* amtInML 12 2 right
*
* Floating-point numbers are displayed with a fixed decimal place.
*
* Amounts have their units placed after them
* c for cups
* ml for milliliters
*
* output - output stream to send data to
* ingredient - ingredient name
* amtInCups - amount in cup units
* amtInML - amount in milliliter units
*
*/
void formatIngredientOutput(ostream &output, string ingredient, double amtInCups, double amtInML)
{
output << setw(35) << left << ingredient;
output.precision(2);
output << setw(12) << fixed << right << amtInCups << "c";
output << setw(12) << fixed << right << amtInML << "ml";
output << endl;
}
/*
* Processes a single line from the recipe. Reads values from the input stream,
* converts the values into the correct serving size and units, and writes the values
* to the output stream.
*
* The function also returns the amount of the ingredient in the desired serving size (cups).
* (This will be useful for calculating the total amount.)
*
* Ingredients are assumed to be an a single line (and may have spaces).
* Amounts are also on a single line. After reading in the amount, everything else on the line
* should be ignored.
*
* inputStream - input data
* outputStream - output
* changeAmt - % of change between the original and desired serving sizes
*
* returns amount of ingredient in desired serving size (cups)
*/
double processIngredient(istream &inputStream, ostream &outputStream, double changeAmt)
{
// read name
string ingredients;
getline (inputStream, ingredients);
// read amount
double val;
inputStream >> val;
inputStream.ignore (100, '\n');
val = convertAmtByServings (val, changeAmt);
//output the result
formatIngredientOutput(outputStream, ingredients, val, convertCupstoMilliliter(val));
return val;
}
//5 ingredients
//track total amounts
/*
* Converts a recipe in terms of serving size and units. Also prints the
* total amount of ingredients in the course.
*
* The original and desired amount of servings should be read in first
* (in that order). Everything on the line after the desired amount should
* be ignored.
*
* The five lines of ingredients should be processed and a total printed.
* The total should follow the same format as that of the ingredients. (See
* formatIngredientOutput)
*
* inputStream - input data
* outputStream - output
*/
void convertRecipe(istream &inputStream, ostream &outputStream)
{
// input
int org, desired;
inputStream >> org >> desired;
inputStream.ignore (1000, '\n');
double changeAmt = changeServings(org, desired);
// process
// call procesIngredient 5 times
double total = 0;
for (int i = 0; i < 5 ; i++)
{
total += processIngredient(inputStream, outputStream, changeAmt);
}
// output
formatIngredientOutput(outputStream, "Total:", total, convertCupstoMilliliter(total));
}
```