Added calculator modes functionality

src/main/c/main_taschenrechner.c

@@ -20,3 +20,31 @@ int multiply(int a, int b) {
 int divide(int a, int b) {
     return a / b;
 }
+
+int mode(int userChoice){
+
+    switch(userChoice) {
+
+        case 1:return 1; // Basic mode
+        break;
+
+        case 2:return 2; // Scientific mode (Trigonomertic functions, Logarithm and exponential functions.)
+        break;
+
+        case 3:return 3; // Graph mode (Draw and visualize functions.)
+        break;
+
+        case 4:return 4; // Programming mode (Binary , octal and hexadecimal )
+        break;
+
+        case 5:return 5; // Unit converter mode (length, weight volume etc.)
+        break;
+
+        case 0: return 0; // printf("Exiting the calculator.\n");
+        break;
+        
+        default: return -1; // printf("Invalid choice. Please try again.\n");
+
+    }
+
+}

src/main/c/taschenrechner.h

@@ -9,4 +9,6 @@ int multiply(int a, int b);
 
 int divide(int a, int b);
 
+int mode(int userChoice);
+
 #endif // TASCHENRECHNER_H