1. KUKUM Sem2-05/06EKT120: Computer Programming1 Week 11 – Files

2. KUKUM Sem2-05/06EKT120: Computer Programming2 Introduction Almost all of the program developed before this is interactive In interactive environment, input is via keyboard and output is via screen/monitor This type of processing is not suitable if it involves huge amount of input or output to be entered or be displayed on the screen at one time Therefore, file processing can solve the problem mentioned

3. KUKUM Sem2-05/06EKT120: Computer Programming3 File Declaration  To implement file processing in C program, need to #include FILE *in_file; FILE *out_file; in_file and out_file are known as internal file name

4. KUKUM Sem2-05/06EKT120: Computer Programming4 Opening File and fopen function Each file must be opened before it is processed While opening the file, external file name need to be related to the internal file name using fopen function. Format: internal_filename =fopen(external_filename, mode); Internal file name is the name that the C system uses to identify a file among others that a program might process External file name is the name given at “save file as” outside the program e.g. “student.dat”, “student.out” etc Mode is used to open file

5. KUKUM Sem2-05/06EKT120: Computer Programming5 File Mode Basics mode are: “r” : open file to read “w” : open file to write “a” : append data to the end of an already existing file “r+” : open and create file to update, i.e. read and write; did not overwrite previous output “w+” :open and create file for update; overwrite “a+” : append; open or create file for update

6. KUKUM Sem2-05/06EKT120: Computer Programming6 Opening File and fopen function-example FILE *in_file; FILE *out_file; in_file = fopen(“student.dat”, “r”); out_file = fopen(“student.out”, “w”);

7. KUKUM Sem2-05/06EKT120: Computer Programming7 File Open Verification There is a possibility opening file fails. Maybe the particular file does not exist Therefore need to check or verify whether the file is successfully opened If file fails to open, need to stop the program, use exit(-1); if (in_file == NULL) {printf(“File fails to open\n”); exit(-1); }

8. KUKUM Sem2-05/06EKT120: Computer Programming8 File Open Verification-cont You can also combine open file and file verification if ((in_file = fopen(“student.dat”, “r”)) == NULL) { printf(“File fails to open\n”); exit(-1); }

9. KUKUM Sem2-05/06EKT120: Computer Programming9 Closing File and fclose function Each opened file need to be closed Format: fclose(internal_filename); e.g fclose(in_file); fclose(out_file);

10. KUKUM Sem2-05/06EKT120: Computer Programming10 Check for End-of-File and the feof function Usually you don’t know how many data you want to read from file Therefore, need to check whether you have reach end of file Format: feof(internal_filename)

11. KUKUM Sem2-05/06EKT120: Computer Programming11 Check for End-of-File and the feof function-example FILE *in_file; in_file = fopen(“student.dat”, “r”); if(in_file == NULL) { printf(“Error opening file\n”); exit(-1); } while(! feof(in_file)) { //stmt to process data } fclose(in_file);

12. KUKUM Sem2-05/06EKT120: Computer Programming12 Reading Data from Text Files Format fscanf(internal file name, format control string, input list); fscanf(in_file, “%d”, &marks);  fgetc(internal file name); ch = fgetc(in_file);  fgets(string variable, size, internal file name); fgets(name, 10, in_file);

13. KUKUM Sem2-05/06EKT120: Computer Programming13 Writing Data to Text File Format fprintf(internal file name, format control string, output list); fprintf(out_file, “%d”, marks);  fputc(character expression,internal file name); fputc(ch, out_file); fputc(“4”, out_file);  fputs(string expression, internal file name); fputs(name, out_file); fputs(“makan”, out_file);

14. KUKUM Sem2-05/06EKT120: Computer Programming14 Sample Program #include int main(void) { FILE *in_file; FILE *out_file; int marks, total=0, count = 0; float avg; in_file = fopen("student.dat", "r"); out_file= fopen("student.out", "w"); if(in_file == NULL) { printf("Error opening file\n"); exit(-1); } while(!feof(in_file)) { fscanf(in_file,"%d",&marks); ++count; total = total + marks; fprintf(out_file, " %d ",marks); } avg = total /count; fprintf(out_file, "\n%.2f\n", avg); fclose(in_file); fclose(out_file); return 0; }//main

15. KUKUM Sem2-05/06EKT120: Computer Programming15 Sample input file and output file 50 60 70 80 90 44 55 66 77 88 24 56 79 50 77 student.dat 50 60 70 80 90 44 55 66 77 88 24 56 79 50 77 64.00 student.out

16. KUKUM Sem2-05/06EKT120: Computer Programming16 End Week 10 – Files (1) Q & A!