C++: Using multiple conditions in switch statements - c++

Question

I am in a beginning C++ programming class and I need help with nesting switch statements and using multiple conditions, because I have to translate a program I already wrote from if/else statements to switch statements, because I didn't know I was supposed to use the switch statement.
For example, how do I change something like:
if (temperature >= -459 && temperature <= -327)
{
cout << "Ethyl Alcohol will freeze.\n";
}
else if (temperature >= -326 && temperature <= -30)
{
cout << "Water will freeze.\n";
}
else if ...
{
}
else
{
}
Into a switch/case statement? I can get the first level, but how do I nest and have multiple conditions like the temperature statements above?

Answer 1

Switch statements work like this:
int variable = 123; // or any other value
switch (variable)
{
case 1:
{
// some code for the value 1
break;
}
case 12:
{
// some code for the value 12
break;
}
case 123:
{
// some code for the value 123
break;
}
case 1234:
{
// some code for the value 1234
break;
}
case 12345:
{
// some code for the value 12345
break;
}
default:
{
// if needed, some code for any other value
break;
}
}

Answer 2

First of all, this question is in C and not in C++. C++ inherited most of the C language, including the switch-case.
You can't do this with a switch, unless you start enumerating all the values one by one, like this:
switch (temperature) {
case -459:
case -458:
....
case -327: <do something>; break;
case -326:
.....
}
This is because in C, switch-case is simply translated to a series of if-goto statements, with the cases just being the labels.

Answer 3

In your case, your stuck with an if-else-if ladder.
You could use a lookup table that has temperatures and the text to print:
struct Temperature_Entry
{
int min_temp;
int max_temp;
const char * text_for_output;
};
static const Temperature_Entry temp_table[] =
{
{-459, -327, "Ethyl Alcohol will freeze.\n"},
{-326, -30, "Water will freeze.\n"},
};
static const unsigned int entry_count =
sizeof(temp_table) / sizeof(temp_table[0]);
//...
int temperature;
for (unsigned int i = 0; i < entry_count; ++i)
{
if ( (temperature >= temp_table[i].min_temp)
&& (temperature < temp_table[i].max_temp))
{
std::cout << temp-table[i].text_for_output;
}
}

Answer 4

As many have pointed out, you cannot use switch case for ranges and dynamic formulas. So if you want to use them anyway, you will have to write a function which takes a temperature and returns a temperature range out of a pre-known set of temperature ranges. Then, finally, you can use a switch/case for the temperature ranges.
enum TemperatureRange { FrigginCold, UtterlyCold, ChillinglyCold, Frosty, ... };
TemperatureRange GetRange( int temperature );
// ...
switch( GetRange( temperature ) )
{
case FrigginCold: cout << "The eskimos vodka freezes."; break;
case UtterlyCold: cout << "The eskimo starts to dress."; break;
// ...
}