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In the last lesson, you learned how to start a program, compile it, and run it. Now, time to learn some basic C++ programming.
First lets analyse the code from the previous section:
#include <iostream.h>
#include <iomanip.h>
int main()
{
cout<<"Hello World"<<endl;
return 0;
}
The #include
statements are library files. Cout, endl, (and later cin) are functions and you have to have the first two lines in every
basic C++ program. Function will be discussed in the next lesson. Libraries will be discussed at a later time. If you want
to know about it now, feel free to ask during the club meetings.
int main()
{
}
is the main function. Everything between the { and } will be done first in every
C++ program. main will be discussed in detail later too, right now, just know that you need it there.
Now, the next thing is the cout<<"Hello World"<<endl;
cout is a function that prints whatever is after it onto the computer screen. It is similar to the print statements in java
and python. "Hello World" is a string, or something like a sentence. Strings
have to be in "". endl is a stream manipulator. It addes a new line character
(like when you press enter on a keyboard).
The return 0; statement is one of those things that are always needed
as well, so just put that there for now. Also notice that at the end of each line, there is a ;
You need that there at the end of each C++ line (except the includes and functions), like in java. C++ is also case-sensitive,
which means if you wrote int Main() or Cout<<"Hello
World"<<endl; it would not work.
NOTE IF YOU ARE USING THE NEW DEV-CPP (5.0): Dev-C++ will report a few warnings if you use "antiquated headers" such
as <iostream.h> or <iomanip.h>. You can ignore these warnings and the program will still run. (but if you have
an error, it will not compile)
Data Types:
For now, heres are some basic data types.
int
an integer. There is no decimals. It includes numbers such as 0, 1, 2, 3
double a float,
or basically any number. Such as 5.1, 7.0, or 15.532
char a
character, such as 'a', 'b', 'y', 'z'. Note characters have to be between ' and '
string a string,
something like "Hello World". (Also note that in dev-cpp, strings are red)
Cin:
Here is a sample code:
#include <iomanip.h>
#include <iostream.h>
int main()
{
int x, z;
int y;
cout<<"Enter two integers:
";
cin>>x>>y;
//this is a comment.
//Everything i type after these two /s will not be compiled
z = 5;
cout<<"x = "<<x<<"
y = "<<y<<" z = "<<z<<endl;
double a;
cout<<"Enter"<<"
a "<<"decimal integer: ";
cin >> a;
cout<<"a = "<<a<<endl;
char c;
cout<<"Enter a character: ";
cin >> c;
cout<<"c = "<<c<<endl;
return 0;
}
To use a data type, you must declare it (like in line 5, 9, 13). You give it a value (like with int z) or let the user
input the value with the function cin.
C++ supports chaining. There are many examples of chaining in this program.
cout<<"x = "<<x<<" y = "<<y<<" z = "<<z<<endl;
could have been written as
cout<<"x = ";
cout<<x;
cout<<" y = ";
cout<<y;
cout<<" z = ";
cout<<z;
cout<<endl;
but programmer (on average) are lazy and wont do something like that.
Also note that a statement such as cout<<z; will output the value
of z;
Similarly, int x, z; can be written as
int x;
int z;
Looking at the declaration int x; This is a variable (as opposed to
constants). This means that you can change the value of x. The int in front of it means that it is a variable integer. x is
a variable name, or identifier. You can call it whatever you like, for example: int
first_integer or int hello3 or something. But the variable name must
start with a character and it cannot contain special characters, such '#', '%', '*', ' ' (a space), etc. For example,
int first integer, int 3hello,
or x# are illegal integer declarations.
Another rule is that your identifier can not match any key word of the C++ language nor your compiler's specific
ones since they could be confused with these. For example, the following expressions are always considered key words according
to the ANSI-C++ standard and therefore they must not be used as identifiers:
asm, auto, bool, break, case, catch, char, class, const, const_cast,
continue, default, delete, do, double, dynamic_cast, else, enum, explicit, extern, false, float, for, friend, goto, if, inline,
int, long, mutable, namespace, new, operator, private, protected, public, register, reinterpret_cast, return, short, signed,
sizeof, static, static_cast, struct, switch, template, this, throw, true, try, typedef, typeid, typename, union, unsigned,
using, virtual, void, volatile, wchar_t
//this is a comment.
//Everything i type after these two /s will not be compiled
like it says, this is a comment. Sometimes programmers like to leave comments in their code so that the reader can follow
his/her code better. Everything after the // will be ignored by the compiler.
String declarations are a bit harder and will be discussed later
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