C++ code to test for positive/negative using switch and "?:" - c++

Question

I am tasked with writing a code to test whether a number is positive, negative, or zero using switch and "?:". Here's what I have. Negative values don't seem to work and I can't figure out how to implement zero. In fact, I don't really quite understand how the whole case1, case2 and switch syntax and how it works in general.
#include <iostream>
using namespace std;
int main()
{
int a;
int b;
cout << "Please enter the value to be tested: ";
cin >> a;
(a > 0) ? (b = 1) : (b = 2);
switch (b)
{
case 1:
cout << "The given value is positive." << endl;
break;
case 2:
cout << "The given value is negative." << endl;
break;
}
return 0;
}

Answer 1

Switch Statement:
The switch statement provides a convenient alternative to the if when
dealing with a multi-way branch. Suppose we have some integer value
called test and want to do different operations depending on whether
it has the value 1, 5 or any other value, then the switch statement
could be employed
Syntax:
switch(expression resulting to integer literals/integer literals/enumeration types/){
case constant-expression :
statement(s);
break; //optional
case constant-expression :
statement(s);
break; //optional
// you can have any number of case statements.
default : //Optional and one default statement can be present for a switch
statement(s);
}
The following rules apply to a switch statement:
The expression used in a switch statement must have an integral or
enumerated type, or be of a class type in which the class has a
single conversion function to an integral or enumerated type.
You can have any number of case statements within a switch. Each case
is followed by the value to be compared to and a colon.
The constant-expression for a case must be the same data type as the
variable in the switch, and it must be a constant or a literal.
When the variable being switched on is equal to a case, the
statements following that case will execute until a break statement
is reached.
When a break statement is reached, the switch terminates, and the
flow of control jumps to the next line following the switch
statement.
Not every case needs to contain a break. If no break appears, the
flow of control will fall through to subsequent cases until a break
is reached.
A switch statement can have an optional default case, which must
appear at the end of the switch. The default case can be used for
performing a task when none of the cases is true. No break is needed
in the default case.
It works as follows:-
The expression, just test in this case, is evaluated.
The case labels are checked in turn for the one that matches the
value.
If none matches, and the optional default label exists, it is
selected, otherwise control passes from the switch compound statement
If a matching label is found, execution proceeds from there. Control
then passes down through all remaining labels within the switch
statement. As this is normally not what is wanted, the break
statement is normally added before the next case label to transfer
control out of the switch statement.
One useful exception occurs when you want to do the same
processing for two or more values. Suppose you want values 1 and
10 to do the same thing, then:-
case 1 :
/*.
any number of cases
.
*/
case 10:
// Process below statements for case 1 to 10
break;
works because the test = 1 case just "drops through" to the next section.
Conditional Operator:
The ternary operator (?:) is a very useful conditional expression used in C and C++. It's effects are similar to the if statement but with some major advantages.
The basic syntax of using the ternary operator is thus:
(condition) ? (if_true) : (if_false)
Which is basically the same as:
if (condition)
if_true;
else
if_false;
Therefore if "condition" is true, the second expression is executed ("if_true"), if not, the third is executed ("if_false").
For you Code:
You can use any of the way to find, one way is,
#define POSITIVE (1)
#define NEGATIVE (-(1))
#define ZERO (0)
switch ( ( user_input >= ZERO )? POSITIVE : NEGATIVE )
{
case POSITIVE:
if( user_input == ZERO )
{
cout << "The given value is a Zero." << endl;
}
else
{
cout << "The given value is positive." << endl;
}
break;
case NEGATIVE:
cout << "The given value is negative." << endl;
break;
}