Added display menu functionality

src/main/c/main_taschenrechner.c

@@ -6,7 +6,7 @@
 
 
 int add(int a, int b) {
-    return a+b;
+    return a + b;
 }
 
 int minus (int a, int b){
@@ -47,4 +47,20 @@ int mode(int userChoice){
 
     }
 
+}
+
+
+// display the mode options:
+
+int displayMenu(){
+
+    printf("\nCalculator Modes: \n");
+    printf("\n1: Basic Mode\n");
+    printf("\n2: Scientific Mode (Trigonomertic functions, Logarithm and exponential functions.)\n");
+    printf("\n3: Graph Mode (Draw and visualize functions.)\n");
+    printf("\n4: Programming Mode (Binary , octal and hexadecimal )\n");
+    printf("\n5: Unit converter Mode (length, weight volume etc.)\n");
+    printf("\n0: Exit calculator\n");
+
+    return 1; // return 1 to check if the function works 
 }

src/main/c/taschenrechner.h

@@ -11,4 +11,6 @@ int divide(int a, int b);
 
 int mode(int userChoice);
 
+int displayMenu();
+
 #endif // TASCHENRECHNER_H