I know what you are talking all along. I cannot make it work because the code vector<int>numSold(defaultNSold) cannot work in all situation, maybe that's answer to my question already, I cannot use this to copy vector in the function where I have to define the vector in the function parameters.Jarvis323 said:You can't make it work because it doesn't make any sense. If you want a new variable, then just use a different name. It won't be the same variable of course. It doesn't make a difference whether it's inside a function or not, you can't use the same name for two different variables. If it worked for you outside a function, then that's not what you did. Here are some examples.
C:// this is wrong vector< int > x; vector< int > & y = x; vector< int > y( d ); // the name y is already used // this is also wrong vector< int > x; vector< int > x; // the name x is already used // this is also wrong vector< int > x; vector< int > x( d ); // the name x is already used // this is also wrong vector< int > x; vector< int > x = d;// the name x is already used // this is correct vector< int > x = d; // this is correct and exactly equivalent to the last version vector< int > x (d); // this is correct as well vector< int > x; x = d;
And it's not because it's a vector either.
C:// this is wrong int x; int & y = x; int y( d ); // the name y is already used // this is also wrong int x; int x; // the name x is already used // this is also wrong int x; int x( d ); // the name x is already used // this is also wrong int x; int x = d;// the name x is already used // this is correct int x = d; // this is correct int x (d); // this is correct as well int x; x = d;
No. It has nothing to do with functions or function parameters, or vectors, or copying. It's much much simpler and the same in every single case. You cannot declare two completely separate variables with the same name in the same scope. It's exactly the same reason you cannot do, int x; int x;, it's not that you cannot use int x; in some special case, it's that the name is already used. You can't do it in any case. Again, the copy constructor is not a copy function. It creates a another variable that is initialized based on the value of the other one.yungman said:I know what you are talking all along. I cannot make it work because the code vector<int>numSold(defaultNSold) cannot work in all situation, maybe that's answer to my question already, I cannot use this to copy vector in the function where I have to define the vector in the function parameters.
I know, it won't work. That's my conclusion already.Jarvis323 said:Here is an analogy that hopefully makes sense.
You go and buy a blender. You read the instructions. It says, to use the blender:
1) unpack the blender from the packaging
2) plug it in
3) press the on button
Later on, after you've already unpacked it and have used it once, you decide to move the blender into a new room. And then you want to turn it on. You read the instructions again how to turn it on. But you find you cannot (1) unpackage the blender, because the packaging is gone. So your solution is you go to the store, buy a new blender, unpack that one, plug that one in, and press its on button. But the old blender is still not on. So you complain. How can I make my old blender work by buying a new blender, unpacking it and turning it on?
The answer is you can't, it's a different blender. The solution is to just plug the old blender in, and it doesn't make sense to unpack and already unpacked blender.
// This program display the title of the product, the unit cost and the total sales in 6 months
// And sort in the order of the highest dollar sales product first to the least.
#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;
void getnumSold(vector<int>&); //To input the number of unit sold in 6 months, you can choose to input the number or use default.
void displayProd(vector<int>&, vector<float>);//displace the list of product and their cost.
void DollarSales(vector<int>&, vector<float>&);//Calculate the total dollar sold for each item.
void sortSales(vector <float>, vector<int>&);// Sort with highest dollar sold first.
void displaySales(vector<int>, vector<float>, vector<int>);// Display in order of the highest dollar sold first.const int Row = 9, ProdCol = 31;
char Prod[Row][ProdCol] = { {"(0)Six Steps to Leadership"}, {"(1)Six Steps to Leadership"}, {"(2)Road to Exellence"},
{"(3)Seven Lessons of Quality"},{"(4)Seven Lessons of Quality"},{"(5)Seven Lessons of Quality"},
{"(6)Teams Are Made, Not Born"}, {"(7)Leadership for the Future"}, {"(8)Leadership for the Future"} };
char Desc[Row][ProdCol] = { {"Book"}, {"Audio CD"}, {"DVD"},
{"Book"}, {"Audio CD"}, {"DVD"},
{"Book"}, {"Book"}, {"Audio CD"} };
float Price[] = { 12.95, 14.95, 18.95, 16.95,
21.95, 31.95, 14.95, 14.95, 16.95 };
int pnAr[] = { 914, 915, 916, 915, 918,// 0, 1, 2, 3, 4
919, 920, 921, 922 };// 5, 6, 7, 8
vector<int>DefaultNSold = { 842, 416, 127, 514, 437, 269, 97, 492, 212 };
int main()
{
vector<int>itemNum = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };//Item number from 0 to 8
vector<int>Sold(DefaultNSold.size());//recieve number sold for each item.
vector<float>totalValue(DefaultNSold.size());
getnumSold(Sold);//passing vector Sold to function getnumSold(). Return of #sold of each item
DollarSales(Sold, totalValue); // pass #sold in vector Sold, and return total sold value of each item.
displayProd(Sold, totalValue);//Show all the tittles of the items
sortSales(totalValue, itemNum);// pass total sold value of each item to sort highest to lowest total $ of items.
// also return the order of the items from highest to lowest for sorting.
displaySales(Sold, totalValue, itemNum);// Display from highest to lowest the total sales of items.
return 0;
}
void getnumSold(vector<int>& numSold)// get and return vector numSold to vector Sold
{
char select;
cout << " Enter y to use default numbers, any other character";
cout << "for entering 6 new numbers: "; cin >> select;
if ((select == 'y') || (select == 'Y'))
{
int row=1;
cout << " In getnumSold, You chose to use default = {";
for (row = 1; row < DefaultNSold.size(); row++)
{
numSold[row - 1] = DefaultNSold[row - 1];
cout << numSold[row - 1] << " ";
}
numSold[row - 1] = DefaultNSold[row - 1];
cout << numSold[row - 1] << "}\n\n";
}
else
{
cout << " You chose to enter 9 new sales number.\n\n";
cout << "Enter number sold for the following\n\n";
for (int row = 1; row <= DefaultNSold.size(); row++)
{
cout << " " << left << setw(35) << Prod[Row-1] << left <<
setw(15) << Desc[row-1] << "$" << Price[row-1] << " is: ";
cin >> numSold[row-1];
}
}
}
void displayProd(vector<int>& Sold, vector<float>totVal)// display the table of selections and price.
{
cout << " In displayProd\n\n";
cout << left << setw(35) << " Product" << setw(15) << "Decription" << setw(10) << "Part num" <<
setw(15) << " Price" << setw(10) << "sold" << setw(17) << "total" << "\n\n";
for (int line = 0; line < Row; line++)
{
cout << " " << left << setw(35) << Prod[line] << left << setw(15) <<
Desc[line] << setw(10) << pnAr[line] << "$" << Price[line] <<
right << setw(10) << Sold[line] << setw(7) <<"$" << left << totVal[line] << "\n\n";
}
}
void DollarSales(vector<int>&Sold, vector<float>&totalValue)// receive vector Sold and vector itemNum.
{ // return to vector Sold.
int size = Sold.size();
for (int element = 0; element < size; element++)
{
totalValue[element] = Price[element] * Sold[element];
//cout << totalValue[element] << "\n\n";
}
}
void sortSales(vector <float>Ar, vector<int>& itemN)// receive vector Sold and vector itemNum.
//function return vector itemN that contain the order of the items sorted from lowest
// total sales to highest.
{
int size = Ar.size();// find the size of the vector.
int startScan = 0, index, temp2;
float temp1;
do
{
index = startScan + 1; // startScan is the first element number, index is the following number.
while (index < size)
{
if (Ar[startScan] < Ar[index])//comparing the lowest number element starting with AR[0] to the rest
{ // one by oneswitch with them if it is higher than the other elements.
temp1 = Ar[startScan]; temp2 = itemN[startScan];
Ar[startScan] = Ar[index]; itemN[startScan] = itemN[index];
Ar[index] = temp1; itemN[index] = temp2;
}
index = index + 1;// to the next lower element to compare, AR[1]->AR[2]-> AR[3]...
}
startScan = startScan + 1;
} while (startScan < (size - 1));
}
void displaySales(vector<int>Sold, vector<float>totalValue, vector<int> itemN)
{
cout << "\n\n\n\n After sorting with the highest dollar amount first \n\n";
cout << left << setw(35) << " Product" << setw(15) << "Decription" << setw(10) << "Part num" <<
setw(15) << " Price" << setw(10) << "sold" << setw(17) << "total" << "\n\n";
int Row = Sold.size();
for (int line = 0; line < Row; line++)
{
cout << " " << left << setw(35) << Prod[itemN[line]] << left << setw(15) <<
Desc[itemN[line]] << setw(10) << pnAr[itemN[line]] << "$" << Price[itemN[line]] <<
right << setw(10) << Sold[itemN[line]] << setw(7) << "$" << left << totalValue[itemN[line]] << "\n\n";
}
}jedishrfu said:The old programming mantra still holds:
_ I can make it fast
- I can make it cheap
- I can make it reliable
pick any two and let me know.
Of course, bosses today will pick two and then ding you on the one they didn't choose.
struct boolmap {
char x:1;
char y:1;
char z:1;
};I assume make it fast meaning the speed, not deliver the program fast. One thing I always told my people, do NOT rush, don't wait until the last minute to do the job. Take the time to do it right, think it out first, don't rush in.Dr Transport said:Never truer words spoken...
float myFloat;
int *pint = &myFloat;What do you think is the type of &myFloat?yungman said:I have a question on initialize pointer. The books said it's illegal to do this:
C++:float myFloat; int *pint = &myFloat;
I understand myFloat is a float, not an int. But the starting address of the variable myFloat is an int. Why can't you initialize int *pint to the address of myFloat?
+1Jarvis323 said:You need to slow down and learn what the code you are writing actually means, not just what you expect it to do.
It's because there generally aren't just plain pointers -- they are almost always pointers to some particular type. In your example, myFloat is a pointer to type float. pint is a pointer to an int. You can't do what you're trying to do without some casts, and even then, you might not get what you expect.yungman said:I understand myFloat is a float, But the starting address of the variable myFloat is an int. Why can't you initialize int *pint to the address of myFloat?C++:float myFloat; int *pint = &myFloat;
float myFloat = 3.75F;
int * pInt = (int *)(&myFloat);
int val = *pInt;Integer!, it's the address of the first byte of the variable myFloat.Jarvis323 said:What do you think is the type of &myFloat?
There's your problem. You don't know what the type is.yungman said:Integer!, it's the address of the first byte of the variable myFloat.
It points to the first byte of the variable, who cares whether it's a float or int or anything.
Is int *pint declare the ADDRESS?Jarvis323 said:There's your problem. You don't know what the type is.
No. It's a variable that can be used to store an address to an int. Its type is (int*).yungman said:Is int *pint declare the ADDRESS?
It's giving you a value of a particular type (int*), that holds the first byte of the variable myfloat.yungman said:Is &myfloat giving you the address of the first byte of the variable of myfloat?
See Mark's post to see why it's not the same thing, and doesn't give the same results whether it's a float or int.yungman said:It's the address, who cares about whether the content of myfloat is a float or int. It's the address.
I am ok if you said you are NOT allow to do this, I can obey that. BUT if the book said int *pint declares an address, and the address of a float is an integer, there is a problem. That's why I post the question here.Jarvis323 said:In C and C++ you have formal types with precise definitions, and the compiler does type checking to make sure the types you are using match up.
yungman said:I am ok if you said you are NOT allow to do this, I can observe that. BUT if the book said int *pint declares an address, and the address of a float is an integer, there is a problem.
Yes, it said int *pint define as address of pointer pint. int *pint initiates a pointer of address.Jarvis323 said:There is no type that is called (address). And integer isn't a type in the C++ type system. The book is not wrong. You just don't understand what a type is.
Right. It also has a type. The book described it, but didn't say what type it is. Where is the problem?yungman said:Yes, it said int *pint define as address of pointer pint. int *pint initiates a pointer of address.
You can have an address pointing to a float variable. All that means is pointing to the first byte of the float variable myFloat. The address is an integer.Jarvis323 said:Right. It also has a type. The book described it, but didn't say what type it is. Where is the problem?
What is its type?yungman said:You can have an address pointing to a float variable. All that means is pointing to the first byte of the float variable myFloat. The address is an integer.
myFloat is a float.Jarvis323 said:What is its type?
The type is (float*). Do you understand that?yungman said:myFloat is a float.
What is the address of the first byte of myFloat? Int or float?
yungman said:The address is an integer.
yungman said:What is the address of the first byte of myFloat? Int or float?
int *pint defines the address of the physical memory location. It HAS TO BE an integer. I designed plenty of real hardware with physical memory. It HAS to be integer. It cannot be a fraction. Take my word on this one. I can show you plenty of example of real schematic of address from A0 to whatever 64bits or 32 bits, it's INTEGER. This is physical hardware.PeterDonis said:No, it isn't. The address is a pointer. "Pointer" and "integer" are different types in C. The fact that you, a human, can take the bits stored in a pointer and interpret them as an integer is irrelevant; C doesn't care and doesn't treat them the same way.
Neither. It's a pointer. A pointer in C is a different type from either int or float.
More specifically, it's a pointer to a float, which is a different type in C from a pointer to an int.
yungman said:int *pint defines the address of the physical memory location. It HAS TO BE an integer.
yungman said:I designed plenty of real hardware with physical memory.
yungman said:It cannot be a fraction.
yungman said:Take my word on this one.
As an example, a char is for storing an integer that is interpreted as an ascii2 character, its type is char.yungman said:int *pint defines the address of the physical memory location. It HAS TO BE an integer. I designed plenty of real hardware with physical memory. It HAS to be integer. It cannot be a fraction. Take my word on this one.
Jarvis323 said:As an example, a char is for storing an integer that is interpreted as an ascii2 character, its type is char.
Yeah, but also confused about what types are. I was trying to get him to understand the distinction between integer and char, or integer and int*.PeterDonis said:The OP's confusion is not about different ways bytes stored in memory can be interpreted. His confusion is about how the addresses of those bytes are interpreted.
Read page 492 to 495 of Gaddis bookPeterDonis said:Sorry, but the actual workings of the C compiler trump your intuitions.
To the C compiler, an address is not an integer, it's a pointer, which is a different type from an integer. No amount of ranting by you will change that.
You can either accept this fact, or you can continue to waste the time of others here by asking questions to which you refuse to accept the correct answers.
We all understand how hardware works. But you don't understand how the C language and the C compiler work. And since you are trying to program in C, not enter hardware instructions directly into the hardware, it is knowledge about how C works that is relevant for this discussion. Knowledge that you do not have, and which you are never going to acquire if you refuse to listen to people who do have it.
Nobody is saying it's a fraction. It's a pointer.
No. The one who needs to be taking the word of others is you. Other people who know far more than you do about how the C language and the C compiler actually work are trying to help you. You need to listen to them, not demand that they listen to you.
If you are unable or unwilling to do this, your thread will end up getting closed. This one exchange has already taken up more time and energy from other posters than it should.
I am trying to distinguish the address of the variable with the content of the variable.Jarvis323 said:Yeah, but also confused about what types are. I was trying to get him to understand the distinction between integer and char, or integer and int*.
The & operator acts like a function, it takes myFloat as an argument and returns something. Both the argument myFloat and the returned value each have a C++ type. The type of the argument is (float). The return type is (float*). Those, with their exact syntax are valid types that the compiler can recognize and parse. The compiler flagged an error because (int*) is not the same type as (float*), and it has been decided by the C++ committee that this type mismatch should throw an error. Why? Because it can be problematic. As in Mark's post, getting the value from a pointer (de referencing) has to interpret the bits as something. Those bits could be encoding a float or an int, the only way to know is if the compiler keeps track of what is supposed to be there. If you really want to convert a value of type (float*), into a type (float*), then you can do type casting as Mark shows, where you ask the compiler to convert/consider the value of type (float *) as a type (int*), and maybe that means that the bits which were encoding 3.75 will now be encoding 1081081856 as far as the compiler knows.yungman said:I am trying to distinguish the address of the variable with the content of the variable.
yungman said:What is the physical address location of a float variable.
yungman said:I am trying to distinguish the address of the variable with the content of the variable.
float *. So the correct way of coding the original snippet of yours that started this subthread, assuming your purpose was to store a pointer to a float variable, would be:float myFloat;
float *pFloat = &myFloat;