refactoring: added comments for better understanding

src/ggT/ggT.c

@@ -2,14 +2,16 @@
 
 
 int ggT(int a, int b){
+    // handles the case if both inputs are 0
     if(a == 0 && b == 0){
         return 0;
-    } else if(a == 0){
+    } else if(a == 0){      // handles the case if first number is 0
         return b;
-    } else if(b == 0){
+    } else if(b == 0){      // handles the case if second number is 0
         return a;
     }
 
+    // Euclidean algorithm with modulo for getting the ggT
     while (b != 0) {
         int temp = b;
         b = a % b;