Avoid duplicate input issue

I'm creating a system for my school assignment. In order to create a file, I need to input data.. The data input cannot be same if it already exist in the record. How to avoid it? Please correct my code.. Thanks..

Code:

void addFlight(void)
{
     system("cls");
     // declare variables
     char flightNo[5];
     char way;
     char departDate[12];
     char departTime[5];
     char origin[15];
     char destination[15];
     char target[10];
     int found = 0;
     float fare;
     FILE *flightFile; // create a file
     
     // open file for writing and reading
     flightFile=fopen("flights.dat","a+");
     
     printf("\n * ADD NEW AIRLINE FLIGHT *\n\n");
     
     fflush(stdin);
     printf("\n Flight Number               : ");
     gets(flightNo);
     
    // avoid duplicate input
     while(!feof(flightFile))
     {
         fscanf(flightFile,"%[^,]%*c %c%*c %[^,]%*c %[^,]%*c %[^,]%*c %[^,]%*c %f%*c \n",flightNo,&way,departDate,departTime,origin,destination,&fare);
         if (strcmp(target,flightNo) != 0)
         {
            printf("\n\n Flight Number               : \n"); 
            gets(flightNo);
         }
          else
              if (flightNo == flightNo)
              {
            printf("\n\n Flight Number is taken, enter a new Flight Number! \n");
            printf("\n\n Flight Number               : \n");
            gets(flightNo);   
              }
     } 

     printf("\n One Way=O / Return=R        : ");
     scanf("%c",&way);
     fflush(stdin);
     
     printf("\n Departure Date [dd-mm-yyyy] : ");
     gets(departDate);
     fflush(stdin);
     
     printf("\n Departure Time [HH.MM]      : ");
     gets(departTime);
     fflush(stdin);
     
     printf("\n Origin                      : ");
     gets(origin);
     fflush(stdin);
     
     printf("\n Destination                 : ");
     gets(destination);
     fflush(stdin);
     
     printf("\n Ticket Fare                 : B$ ");
     scanf("%f",&fare);
     fflush(stdin);

     fprintf(flightFile,"%s, %c, %s, %s, %s, %s, %.2f \n",flightNo,way,departDate,departTime,origin,destination,fare);
     fclose(flightFile); // close the file
     
     printf("\n\n");
     system("pause");
     flightMenu();
     
}

This doesn't create a file. It merely creates a pointer to a file descriptor.

Code:

FILE *flightFile; // create a file

This could create a file, but you should check for it.

Code:

flightFile=fopen("flights.dat","a+");

Don't use fflush() on input streams. What it does is only defined for output streams.

Code:

fflush(stdin);

Code:

if (flightNo == flightNo)

The following code makes just about as much sense as yours.

Code:

// check if this program is running in our Universe
if( !( 1 == 1 ) )
{
    panic();
}

To check if an entry doesn't already exist, you need to build a list of existing entries, and then check all new entries against that list. It is not the best solution, but it is easily doable and very likely what is expected of you.

The advantage of this approach would be that you only need to read the input file once. You can add as many new entries as needed after that. As long as you remember to add the new entries to the list of existing entries in order to correctly check consecutive new entries, that is.

could you please correct the coding for me? :/

I could and I won't. This is your assignment.

I've been thinking since morning and it's due tomorrow.. Thanks anyway..

Anyone else is willing to help me.. please..

Another sad, clueless cross-poster