# Programming Fundamentals/Conditions/PHP

## conditions.php

```<?php

// This program asks the user to select Fahrenheit or Celsius conversion
// and input a given temperature. Then the program converts the given
// temperature and displays the result.
//
// References:
//     https://www.mathsisfun.com/temperature-conversion.html
//     https://en.wikibooks.org/wiki/PHP_Programming

function get_choice()
{
printf("Enter F to convert to Fahrenheit or C to convert to Celsius: ");
return \$choice;
}

function process_celsius()
{
\$temperature = get_temperature("Fahrenheit");
\$result = calculate_celsius(\$temperature);
display_result(\$temperature, "Fahrenheit", \$result, "Celsius");
}

function process_fahrenheit()
{
\$temperature = get_temperature("Celsius");
\$result = calculate_fahrenheit(\$temperature);
display_result(\$temperature, "Celsius", \$result, "Fahrenheit");
}

function get_temperature(\$label)
{
echo "Enter " . \$label . " temperature: ";
return \$temperature;
}

function calculate_celsius(\$fahrenheit)
{
\$celsius = (\$fahrenheit - 32) * 5 / 9;

return \$celsius;
}

function calculate_fahrenheit(\$celsius)
{
\$fahrenheit = \$celsius * 9 / 5 + 32;

return \$fahrenheit;
}

function display_result(\$temperature, \$from_label, \$result, \$to_label)
{
echo \$temperature . "° " . \$from_label . " is " . \$result . "° " . \$to_label . "\n";
}

function main()
{
// main could either be an if-else structure or a switch-case structure

\$choice = get_choice();

// if-else approach
if(\$choice == 'C' || \$choice == 'c')
{
process_celsius();
}
else if(\$choice == 'F' || \$choice == 'f')
{
process_fahrenheit();
}
else
{
echo "You must enter C to convert to Celsius or F to convert to Fahrenheit!";
}

// switch-case approach
switch(\$choice)
{
case 'C':
case 'c':
process_celsius();
break;
case 'F':
case 'f':
process_fahrenheit();
break;
default:
echo "You must enter C to convert to Celsius or F to convert to Fahrenheit!";
}
}

main();

?>
```

## Try It

Copy and paste the code above into one of the following free online development environments or use your own PHP compiler / interpreter / IDE.