feat: add Celsius to Fahrenheit conversion (#1129)

* feat: added celcius_to_fahrenheit.c

* docs: added comment to 1st test

* updating DIRECTORY.md

* fix: changed spelling of 'celcius' to 'celsius'

* updating DIRECTORY.md

* Update conversions/celsius_to_fahrenheit.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update conversions/celsius_to_fahrenheit.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* chore: apply suggestions from code review

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>

conversions/celsius_to_fahrenheit.c

@@ -0,0 +1,74 @@
+/**
+ * @file
+ * @brief Conversion of temperature in degrees from [Celsius](https://en.wikipedia.org/wiki/Celsius)
+ * to [Fahrenheit](https://en.wikipedia.org/wiki/Fahrenheit).
+ * 
+ * @author [Focusucof](https://github.com/Focusucof)
+ */
+
+#include <assert.h> /// for assert
+#include <stdio.h>  /// for IO operations
+
+/**
+ * @brief Convert celsius to Fahrenheit
+ * @param celsius Temperature in degrees celsius double
+ * @returns Double of temperature in degrees Fahrenheit
+ */
+ double celcius_to_fahrenheit(double celsius) {
+    return (celsius * 9.0 / 5.0) + 32.0;
+ }
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void test() {
+    // 1st test
+    double input = 0.0;
+    double expected = 32.0;
+
+    double output = celcius_to_fahrenheit(input);
+
+    // 1st test
+    printf("TEST 1\n");
+    printf("Input: %f\n", input);
+    printf("Expected Output: %f\n", expected);
+    printf("Output: %f\n", output);
+    assert(output == expected);
+    printf("== TEST PASSED ==\n\n");
+
+    // 2nd test
+    input = 100.0;
+    expected = 212.0;
+
+    output = celcius_to_fahrenheit(input);
+
+    printf("TEST 2\n");
+    printf("Input: %f\n", input);
+    printf("Expected Output: %f\n", expected);
+    printf("Output: %f\n", output);
+    assert(output == expected);
+    printf("== TEST PASSED ==\n\n");
+
+    // 3rd test
+    input = 22.5;
+    expected = 72.5;
+
+    output = celcius_to_fahrenheit(input);
+
+    printf("TEST 3\n");
+    printf("Input: %f\n", input);
+    printf("Expected Output: %f\n", expected);
+    printf("Output: %f\n", output);
+    assert(output == expected);
+    printf("== TEST PASSED ==\n\n");
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    test();  // run self-test implementations
+    return 0;
+}