Add function struct and tags for person tag and course tag

Add header functions

work1/single.c

@@ -1,7 +1,27 @@
 #include "stdio.h"
 #include "stdlib.h"
 
-int main() {
+struct person_tag {
+    char name[20];
+    char id[10];
+};
+
+struct course_tag {
+    char course_name[20];
+    int no_of_units;
+    int marks[4];
+    float avg;
+};
+
+void display_students(void);
+void search_student(void);
+void find_maximum(void);
+void find_failed(void);
+void update_file();
+void read_file();
+void quite();
+
+int main(void) {
     printf("Welcome!");
 
     printf("Goodbye!");