Write a C program that takes a celsius value as input and convert it to a fahrenheit value.

**What is Celsius?**

**Celsius** is a unit used to measure the temperature on Celsius scale. It was developed by Swedish astronomer Anders Celsius and is often denoted by **°C**(degree Celsius).

**What is Celsius scale in C?**

**Celsius scale** is based on freezing and boiling point of water at 1 atm pressure that is **0°** and **100°C** respectively. The scale is divided into 100 divisions between the two extreme temperatures of water and hence it is often referred to as centigrade scale.

**What is Fahrenheit?**

**Fahrenheit** is also a unit to measure the temperature on Fahrenheit scale. It was developed by polish physicist Daniel Gabriel Fahrenheit in 1724 and is often denoted by symbol **°F**(degree Fahrenheit).

**What is Fahrenheit scale?**

On **Fahrenheit scale** the freezing and boiling point of water is defined at **32°** and **212°F** respectively with 180 divisions between them.

**Celsius to Fahrenheit conversion in C:**

The conversion of Celsius to Fahrenheit takes place by the given relation –

Which on further simplifying gives – \(\frac{C}{100}=\frac{F-32}{180}\)

\(C=\frac{5(F-32)}{9}\) Or \(F = \frac{9C}{5} + 32\)

Here, F is temperature in Fahrenheit and C is temperature is Celsius.

**Example:**

Let’s say the question goes like convert 37°C to Fahrenheit

So using the equation –

Substituting the values of C and solving the equation for F we have,

\(F = \frac{333}{5} + 32\)

F = 66.6 + 32

F = 98.6°F

Let’s discuss different ways to convert celsius to fahrenheit in C language.

- Convert Celsius to Fahrenheit in C using Naive Approach
- Convert Celsius to Fahrenheit in C using Function

This approach simply converts the celsius to fahrenheit using the formula i.e. **Fahrenheit = (9 * Celsius)/5 + 32**

**Example:**

Assume the temperature in Celsius is 100, then

\(F = \frac{9C}{5} + 32\)

\(F = \frac{9×100}{5} + 32\)

\(F = \frac{900}{5} + 32\)

F = 180 + 32

F = 212°F

Here is source code of the C program to convert celsius to fahrenheit using formula. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

`/*`

`* C program to convert celsius to fahrenheit using formula`

`*/`

`#include <stdio.h>`

int main()

`{`

double Fahrenheit;

double Celsius;

printf ("Enter the Temperature in Celsius: ");

scanf ("%lf", &Celsius);

Fahrenheit = (9 * Celsius) / 5 + 32;

printf ("The Temperature in Fahrenheit is: %.2lf\n", Fahrenheit);

return 0;

`}`

1. Declare the double variable **Celsius** and **Fahrenheit** and take the input for temperature in Celsius using **scanf** function.

2. Calculate the temperature in Fahrenheit using the formula “**Fahrenheit = (9 * Celsius) / 5 + 32;**” and store it in variable named **Fahrenheit**

3. Finally, print the result using **printf** function.

**Note:**

- The declared data-type of variable is double because temperatures can be in decimal and the format specifier for double is %lf.
- %.2lf in above code prints the output till two decimal digits.

**Time Complexity: O(1)**

The Time Complexity of above program is O(1), as the code is taking constant time in calculating the result based on the formula.

**Space Complexity: O(1)**

The space complexity is O(1), as no any extra/auxiliary space is required in the program.

**Testcase 1:** In this case, we are entering the Celsius value “100” as input.

Enter the Temperature in Celsius: 100 The Temperature in Fahrenheit is: 212.00

**Testcase 2:** In this case, we’re entering “37” as the Celsius value to convert to Fahrenheit.

Enter the Temperature in Celsius: 37 The Temperature in Fahrenheit is: 98.60

In this approach, we convert the celsius value to fahrenheit using function. Functions enhance the code reusability and prevent users from violating the DRY principle which is don’t repeat yourself.

**Example:**

Assume the temperature in Celsius is 0, then

\(F = \frac{9C}{5} + 32\)

\(F = \frac{9×0}{5} + 32\)

\(F = \frac{900}{5} + 32\)

F = 0 + 32

F = 32°F

Here is source code of the C program to convert celsius to fahrenheit using formula. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

`/*`

`* C program to convert celsius to fahrenheit using function`

`*/`

`#include <stdio.h>`

void Celsius_to_Fahrenheit(double Celsius)

`{`

double Fahrenheit;

Fahrenheit = (9 * Celsius) / 5 + 32;

printf ("The Temperature in Fahrenheit is: %.2lf\n", Fahrenheit);

`}`

int main()

`{`

double Celsius;

printf ("Enter the Temperature in Celsius: ");

scanf ("%lf", &Celsius);

Celsius_to_Fahrenheit(Celsius);

return 0;

`}`

1. Create a function name **Celsius_to_Fahrenheit** which take temperature in **Celsius** as parameter.

2. Calculate the temperature in Fahrenheit using the formula “**Fahrenheit = (9 * Celsius) / 5 + 32;**” and store it in variable named **Fahrenheit**

3. The return type of function is void as it does not return anything.

4. In driver program, declare double variable named **Celsius** and took the input using **Scanf** function and called the function **Celsius_to_Fahrenheit** by passing the temperature in Celsius as parameter

5. Print the result that is the temperature in Fahrenheit for the given temperature in Celsius using **printf** function.

**Time Complexity: O(1)**

The Time Complexity of above program is O(1), as the code is taking constant time in calculating the result based on the formula.

**Space Complexity: O(1)**

The space complexity is O(1), as no any extra/auxiliary space is required in the program.

**Testcase 1:** In this case, we’re entering “0” as the Celsius value to convert to Fahrenheit.

Enter the Temperature in Celsius: 0 The Temperature in Fahrenheit is: 32.00

**Testcase 2:** In this case, we are entering the Celsius value “12” as input.

Enter the Temperature in Celsius: 12 The Temperature in Fahrenheit is: 53.60

**Conclusion: **

- Various temperature scales not only help to measure the temperatures but also to mathematically study them and perform important calculations based upon them.
- Celsius scale is quite popular in India whereas Fahrenheit Scale is popular in United States.

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