database - How to open a file with a user inputted variable in C? -

i'm writing pos program school assignment. i'm using multiple txt files database. program suppose allow user enter sku number (e.g. 123) open txt file in database (e.g. database/123.txt). pull info txt file such price , allow user add multiple files , end total. user can add database creating new skus. able view transaction history. issue having can't seem figure out how record number user , use number open text file beginning number. (e.g. use enters 123 123.txt opened.)

here section of code need with:

// function start transaction int transaction(void) {     // define variables     char buf[1000], ndatabase[100];     float nprice[500], ntotal;      // instructions     printf("you have started transaction.\n");     printf("enter sku number below.\n");     printf("enter 0 complete transaction.\n");       // begin loop here         {         file *ptr_file;          // record sku number         /*remove test tools later*/         printf("we r here\n");         scanf("enter sku: %c\n", &ndatabase);         printf("now r here\n");           // open database file           /*change location later*/         ptr_file = fopen("database/123.txt", "r");         // if file not found return 1         if (!ptr_file)         {             printf("could not match sku number.\n");             return 1;         }           while (fgets(buf, 1000, ptr_file) != null)             printf("%s\n", buf);         scanf("%s", &nprice[0]);         // close file             fclose(ptr_file);              while (ndatabase == 0);                  ntotal = nprice[0] + nprice[1];                 printf("your total is: $%.2f\n", &ntotal);                 return 0;      } } 

printf( "enter sku: " ) ;  // <-- scanf if input, prompt must output separately scanf( "%s\n", ndatabase); //       ^     ^ //       |     |_no & here - ndatabase array //       | //       |_accept string not character 

then might form complete file name sprintf, e.g.

char filename[max_fname] ; sprintf( filename, "database/%s,txt", ndatabase ) ; 

be aware no error checking or overrun protection performed above - may want consider adding some.