added logic to ConArea and Unittest for the function

src/main/c/ConvertMode.c

@@ -164,6 +164,18 @@ double getValue(int choice) {
 
             printf("\nThe convertet result is %dlf %d", result, Data[endingUnit]);
             break;
+
+        case 11://char Distance[] = { 'mm', 'cm', 'm', 'km', 'feet/inch', 'miles'};
+            printf("\nEnter what the Unit is starting with (0 mm, 1 cm, 2 m , 3 km,): ");
+            scanf("%d", &startingUnit);
+
+            printf("\nEnter what the value should it be changed to (0 mm, 1 cm, 2 m , 3 km,): ");
+            scanf("%d", &endingUnit);
+
+            result = ConArea(value, startingUnit, endingUnit);
+
+            printf("\nThe convertet result is %dlf %d²", result, Distance[endingUnit]);
+            break;
         }
     }
 }
@@ -208,14 +220,6 @@ double ConSpeed(double speed, int startingUnit, int endingUnit) {
 */
 
 
-
-
-
-
-double ConArea() {
-
-}
-
 double ConVolume() {
 
 }

src/main/c/main_taschenrechner.c

@@ -189,6 +189,106 @@ double ConMeter(double meter, int startingUnit, int endingUnit) {
     }
 }
 
+double ConArea(double area, int startingUnit, int endingUnit) {
+    switch (startingUnit)
+    {
+    case 0: //mm to x
+        switch (endingUnit)
+        {
+        case 0: //1mm
+            return area;
+            break;
+
+        case 1: //0.01cm
+            return area / 100;
+            break;
+
+        case 2: //0.000001m
+            return area / 1000000;
+            break;
+
+        case 3: //0.000000000001km
+            return area / 1000000000000;
+            break;
+
+        default:
+            break;
+        }
+
+    case 1: //cm to x
+        switch (endingUnit)
+        {
+        case 0: //100
+            return area * 100;
+            break;
+
+        case 1: //1
+            return area;
+            break;
+
+        case 2: //0.0001
+            return area / 10000;
+            break;
+
+        case 3: //0.0000000001
+            return area / 10000000000;
+            break;
+
+        default:
+            break;
+        }
+
+    case 2: //m to x
+        switch (endingUnit)
+        {
+        case 0: //1000000
+            return area * 1000000;
+            break;
+
+        case 1: //10000
+            return area * 10000;
+            break;
+
+        case 2: //1
+            return area;
+            break;
+
+        case 3: //0.000001
+            return area / 1000000;
+            break;
+
+        default:
+            break;
+        }
+
+    case 3:// km to x
+        switch (endingUnit)
+        {
+        case 0: // 1000000000000
+            return area * 1000000000000;
+            break;
+
+        case 1: // 10000000000
+            return area * 10000000000;
+            break;
+
+        case 2: // 1000000 m
+            return area * 1000000;
+            break;
+
+        case 3: //1 km
+            return area;
+            break;
+
+        default:
+            break;
+        }
+
+    default:
+        break;
+    }
+}
+
 double ConMeterToFoot(double distance, int startingUnit, int endingUnit) {
     switch (startingUnit)
     {

src/main/c/taschenrechner.h

@@ -77,4 +77,6 @@ double ConLiterToGallon(double fluid, int startingUnit, int endingUnit);
 
 double ConData(double data, int startingUnit, int endingUnit);
 
+double ConArea(double area, int startingUnit, int endingUnit);
+
 #endif // TASCHENRECHNER_H

src/test/c/test_taschenrechner.c

@@ -88,5 +88,10 @@ void test_ConData(void) {//5 b to kb
     TEST_ASSERT_EQUAL(0.005, result);
 }
 
+void test_ConArea(void) {//5 mm to cm
+    double result = ConData(5, 0, 1);
+    TEST_ASSERT_EQUAL(0.0005), result);
+}
+
 
 #endif // TEST