added logic to ConSpeed and Unittest for the function

src/main/c/ConvertMode.c

@@ -13,7 +13,8 @@ double value, result;
 char Distance[] = { 'mm', 'cm', 'm', 'km', 'feet/inch', 'miles'};
 char Weight[] = { 'mg', 'g', 'kg', 't', 'pounds'};
 char Fluid[] = { 'ml', 'l' };
-char Temp[] = {'celsius', 'fahrenheit'}
+char Temp[] = { 'celsius', 'fahrenheit' };
+char Speed[] = { 'km/h','mp/h' };
 char Data[] = { 'B', 'KB', 'MB', 'GB', 'TB', 'PT' };
 char Time[] = { 'ms', 's', 'min', 'h', 'd', 'w', 'mon', 'y' };
 char currency[] = { 'E', 'D', 'R' };
@@ -114,6 +115,18 @@ double getValue(int choice) {
 
             printf("\nThe convertet result is %dlf %d", result, Distance[endingUnit]);
             break;
+        
+        case 6://'km/h','mp/h'
+            printf("\nEnter what the Unit is starting with (0 km/h, 1 mp/h): ");
+            scanf("%d", &startingUnit);
+
+            printf("\nEnter what the value should it be changed to (0 km/h, 1 mp/h): ");
+            scanf("%d", &endingUnit);
+
+            result = ConSpeed(value, startingUnit, endingUnit);
+
+            printf("\nThe convertet result is %dlf %d", result, Distance[endingUnit]);
+            break;
 
         }
     }
@@ -121,9 +134,7 @@ double getValue(int choice) {
 
 
 
-double ConSpeed() {
 
-}
 
 double ConLiter() {
 

src/main/c/main_taschenrechner.c

@@ -441,6 +441,44 @@ double ConTemp(double temp, int startingUnit, int endingUnit) {
     }
 }
 
+double ConSpeed(double speed, int startingUnit, int endingUnit) {
+    switch (startingUnit)
+    {
+    case 0: //kmh to x
+        switch (endingUnit)
+        {
+        case 0: //kmh to kmh
+            return distance;
+            break;
+
+        case 1: //kmh to mph
+            return distance * 0.621371;
+            break;
+
+        default:
+            break;
+        }
+
+    case 1: //mph to x
+        switch (endingUnit)
+        {
+        case 0: //mph to kmh
+            return distance * 1.60934;
+            break;
+
+        case 1: //mph to mph
+            return distance;
+            break;
+
+        default:
+            break;
+        }
+
+    default:
+        break;
+    }
+}
+
 //..
 // graphMode
 void graphMode() {

src/main/c/taschenrechner.h

@@ -69,4 +69,6 @@ double ConGramToPounds(double weight, int startingUnit, int endingUnit);
 
 double ConTemp(double temp, int startingUnit, int endingUnit);
 
+double ConSpeed(double speed, int startingUnit, int endingUnit);
+
 #endif // TASCHENRECHNER_H

src/test/c/test_taschenrechner.c

@@ -68,5 +68,10 @@ void test_ConTemp(void) {//5 celsius to fahrenheit
     TEST_ASSERT_EQUAL(41, result);
 }
 
+void test_ConSpeed(void) {//5 kmh to mph
+    double result = ConTemp(5, 0, 1);
+    TEST_ASSERT_EQUAL(3.10686, result);
+}
+
 
 #endif // TEST