Conditions give a huge
amount of flexibility to a program; they allow the program to choose for
itself. Well not choose entirely for themselves, but rather for the options
that you give it. Giving the program the ability to choose for itself gives a
tremendous amount of versatility. Without conditions the same program would run
the same over and over again, and what fun is that? The first condition we will
discuss is the most common, the if statement. Here is the syntax.
if (condition)
{
//execute whatever is inside these brackets
}
The condtion inside the
parenthesis is what has the power to choose whether or not to execute. Let us
look at a situation where we have three variable x,y,z. First we will
initialize them and assign them values. In this case if x is greater than y
then the condtions will execute.
int x,y,z;
cin>>x;
cin>>y;
if(x>y)
{
z = x+y;
cout<<z;
}
Once we enter in the
values of x and y the condtion will determine whether or not x is greater than
y if so then z will be given the value of the sum of x and y and then print out
the result. At this point if x is not greater than z than nothing will happen
but we can fix this by simply giving the program another option. This is the
else if.
int x,y,z;
cin>>x;
cin>>y;
if(x>y)
{
z=x+y;
cout<<z;
}
else if (x<y)
{
z=x-y;
cout<<z;
}
As you can probably see
else if just gives the program another option and in this case if x is less
than y then z will given the value of x minus y and then be printed to the
screen. You are given the power to give a program as many conditions as you want
simply by adding as much else if statements as you wish. So in this case what
if x isn't greater or less than y? If we still wanted something to happpen in
this situation then we would just add and else statement to the program.
//Full Working Program
#include
<iostream>
using namespace std;
int main()
{
int x,y,z;
cin>>x;
cin>>y;
if(x>y)
{
z=x+y;
cout<<z;
}
else if (x<y)
{
z=x-y;
cout<<z;
}
else
{
cout<<"x is nor greater or less than y so they must be
equal"<<endl;
}
return 0;
}
If x is not greater or
less than y then the first two condtions will not execute leaving the last
condtion. The else can be thought of as a last resort, notice how it doesn't
even have a condition, this is because the condition for the else statement is
if nothing else executes it will. There are a few different operations that can
be inside a condition here are a few.
< //less than
> //greater
than
<= //less than or
equal to
>= //greater than or
equal to
== //checks to see if
variable is equal to value
=! //checks to see if
variable is not equal to value
Now that we have these
new found tools lets try something new that we couldn't of done before. Lets
build a program that as soon as it starts up is asks you whether or not you
would like to calculate the volume of a right circular cone or the area of a circle.
//Full Working Program
#include
<iostream>
using namespace std;
int main()
{
int x; //integer x to
take in either 1 or 2
double r,h,V,A; //r for
radius, h for height, V for volume, and A for area
cout<<"To calculate the volume of a right circular cone press
1"<<endl;
cout<<"To calcualte the area of a circle press 2"<<endl;
cin>>x;
//bring in the condtions
to determine what calcualtion to execute
if (x==1) //checks to
determine if x is equal to 1
{
cout<<"Please
enter a radius"<<endl;
cin>>r;
cout<<"Please
enter a height"<<endl;
cin>>h;
V=1.0/3.0*3.14159*r*r*h;
//equation for the volume of a right circular cone
cout<<"The radius is "<<r<<" and the height is
"<<h<<endl;
cout<<"so the volume of the right circular cone is
"<<V<<endl;
}
if (x==2) //checks to
determine if x is equal to 2
{
cout<<"Please
enter a radius"<<endl;
cin>>r;
A=3.14159*r*r;
//equation for the area of a circle
cout<<"The radius is "<<r<<" so the area is
"<<A<<endl;
}
else
{
cout<<"Invalid input "<<endl;
}
return 0;
}
This program is very
straight forward first it decides what condtition to execute given by the users
input. If 1 is entered the program will ask for a radius and height and then
give you the volume of right circular cone. If the user enters 2 then the program
will calculate the area of circle once the radius is given. If the user doesn't
input 1 or 2 then the program will tell the user they have entered invalid
input.
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