First post for me! I need help with this code!

[BlueTea]

Hi,

I'm a computer engineering student who happens to be taking his first programming course ever (and my first encounter with programming). I can't really see anything wrong with this code although I suspect that my (char day;) line doesn't make sense or is insufficient. I followed the logic that I use with integers, when I want to tell the program that I'll be going to an integer which belongs to time for example, I do this:

int time;
cout<<"Enter time";
cin>>time;

But I have a feeling this is not the case here:

#include <iostream>
using namespace std;
void main()
{
char day;
int temperature;

cout<<"enter temperature";
cin>>temperature;
cout<<"enter day";
cin>>day;

if ((temperature < -10) && (day == sunday))
{
cout << "Stay home.";
}
else if (temperature < -10) //and day != SUNDAY
{
cout << "Stay home, but call work.";
}
else if (temperature <= 0) //and temperature >= -10
{
cout << "Dress warm.";
}
else //temperature > 0
{
cout << "Work hard and play hard.";
}
}


I copied everything from the first if statement to the last else statement from my book, including commentary, when I compile, it tells me that sunday is an undeclared identifier.

[Albatross]

You see, day is a single character. If you want to compare it with a string, you'll need to #include <string> at the top of your file, and change day to a string. This will also remedy a little problem with how you used cin. :)

Also, sunday is an undeclared identifier. You probably meant to put "sunday" there instead, which is a string literal. :)

Finally, it's int main(), not void main().

Have fun!

-Albatross

P.S: I like your username.

[hanst99]

void main is an abomination and should not be used. You cin into a char, you probably want to cin into a char*. And then you use the comparison operator, which makes no sense for char*.

Oh, and sunday and SUNDAY are different things in C++- SUNDAY is probably a macro.

[BlueTea]

So I can't use char values in bool expressions ?!

[Albatross]

Oh, you can. It's just that if you were to use a char variable you'd be comparing it with a char*, which you can't immediately do with ==, while you can compare an std::string and a char* with ==. Remember: a char stores a single character.

-Albatross

[hanst99]

char* are pointers, so if you would compare two char*, you would check for identity, not for equality.

[BlueTea]

The thing is that in my class, we have yet to reach things such as char*. Also, for some ridiculous reason, my midterm will be on paper, including writing codes, so I'm worried about that.

If I would compare what I have to cover for my midterm in contrast with what you guys know, that would be the following at their utter-most basic levels:

-if else statements

-switch statments

-while and do-while

The text we are using is Absolute C++, and I don't like how the author doesn't write the entire code in his examples.

[hanst99]

Must be some old text book if it tells you to use void main. Though on the other hand, at least it doesn't append a .h to iostream, maybe it's just bad rather than old? Anyways: In C++, you want to work with std::strings rather than with char* whenever possible. Frees you from a major error source you would have otherwise.

[BlueTea]

ahh the thing is, nothing was ever mentioned regarding std::strings or char*, both of these I'm seeing for the first time in this thread. If it helps in any way, we are coding with visual studio 9.0

[hanst99]

"This is a string literal"
'c'/*<-- That is a char*/
char* a; /* is a pointer to char */
string b; /* this is a std::string */

[BlueTea]

Thank you!

[madredcake]

The same program using strings, the important changes are preceded by
//LOOK AT ME
comment

#include <iostream>
//LOOK AT ME 
#include <string>

using namespace std;

int main(){
  //LOOK AT ME 
  string day                         ;
  int    temperature                 ;

  cout << "Enter the temperature \n" ;
  cin  >> temperature                ;
  cout << "Enter the day \n"         ;
  cin  >> day                        ;

  //LOOK AT ME ("sunday" not sunday)
  if ( (temperature < -10) && (day == "sunday") ){

    cout << "Stay home." ;

  //and day != SUNDAY
  } else if (temperature < -10){
    cout << "Stay home, but call work.";

  //and temperature >= -10
  } else if (temperature <= 0){
    cout << "Dress warm.";

  //temperature > 0
  } else {
    cout << "Work hard and play hard.";
  }

  return (0);
}

Works only for "sunday" entered in lowcases.
To put it simply:
char can keep a single character
string can keep a word, a sentence, a paragraph. Bunch of letters followed by Enter.

strings are basically identifiers for text.

Example.

#include <iostream>
#include <string>

using namespace std;

int main(){
  string text;
  text = "I tried to write something wise, but it turned out to be as always.";
  cout << text;
  
  //char* is working in simillar fashion, but, if you can, stay with strings.
  char* text;
  text = (char*)"For the second time I tried to write something wise and I failed again";
  cout << text;
  
  return (0);
}

[hanst99]

madred, you char* part contains an implicit conversion of const char* to char*.

[madredcake]

Edited, one more reason to not use char*
Probably you don't like my casting now...

[hanst99]

Making the conversion explicit is not a solution. A string literal is ALWAYS constant, using it as a non constant char* can lead to anything from subtle bugs like weird results of string operations to serious things like crashes. The real fix would have been to make text constant.

[BlueTea]

I'm really sorry if this is against the rules but I want to post another code over here and I'm confused regarding what it generates. I pulled this code off my book as well.

#include <iostream>
using namespace std;
int main( )
{
int x = 10;
while (x > -1)
{
cout << x << endl;
x=x-3;
}
return 0;
}



Okay so the output for this would be

10
7
4
1

I am confused as to why it wouldn't also generate -2 at the end ??? isn't 1 still larger than -1 ? isn't it supposed to put the new x value of 1 through the expression x=x-3 ? Please explain.



EDIT!!!!:

So after thinking about it, it does turn the x value to -2 but upon repeating the lopp statement, -2 fails to satisfy the while(x>-1) line thus not printing out -2, am I right ?

[guestgulkan]

Yes