Calculate the total from one file, output the average to another file and standard output using fopen() and fscanf_s()/fscanf()


Compiler: Visual C++ Express Edition 2005

Compiled on Platform: Windows Xp Pro with SP2

Header file: Standard

Additional library: none/default

Additional project setting: Set project to be compiled as C

Project -> your_project_name Properties -> Configuration Properties -> C/C++ -> Advanced -> Compiled As: Compiled as C Code (/TC)

Other info:

To do: Calculate the total from one file, output the average to another file and standard output

To show: How to use fopen() and fscanf()/fscanf_s() function to read from a file, process and write the result to another file


Create files named input.txt and output.txt and put them in C:. Fill in some integers in the input.txt for example as shown below.


23 12 33 10 4 6 44 31 7 50


Run the following program.


/* Program to calculate the average of a list of numbers. */

/* calculate the total from one file, output the average */

/* into another file */

#include <stdio.h>

/* for exit() */

#include <stdlib.h>


int main(void)


int value, total = 0, count = 0;

/* fileptrIn and fileptrOut are variables of type (FILE *) */

FILE * fileptrIn, * fileptrOut;

// For testing the files existence

errno_t err = 0, err1 = 0;

// For file names & paths

char filenameIn[50], filenameOut[50];


// Make sure you have already created the file that contains some integers

// at your desired location for this example C:\input.txt that contains 23 12 33 10 4 6 44 31 7 50

printf("Please enter an input filename (use path if needed):\n");

scanf_s("%s", filenameIn, 50);

// Make sure you have already created this empty file, for this example C:\output.txt

printf("Please enter an output filename (use path if needed):\n");

// scanf("%s", filenameOut);

scanf_s("%s", filenameOut, 50);


/* open files for reading, "r" and writing, "w" */

// fopen(filenameIn, "r"), use secure version here

// Test the files existence

err = fopen_s(&fileptrIn, filenameIn,"r");

err1 = fopen_s(&fileptrOut, filenameOut,"w");


if(err !=0 )


printf("\nError opening %s for reading.\n", filenameIn);

exit (1);



printf("\nOpening %s for reading is OK.\n", filenameIn);


if(err1 != 0)


printf("Error opening %s for writing.\n", filenameOut);

exit (1);



printf("Opening %s for writing is OK.\n", filenameOut);


/* fscanf() */

printf("\nThe data:\n");

// EOF != fscanf(fileptrIn, "%i", &value) but using a secure version here

while(EOF != fscanf_s(fileptrIn, "%i", &value))


printf("%d ", value);

total += value;



/* end of while loop */


printf("\nThe total: %d\n", total);

/* Write the average value to the file. */

/* fprintf() */

printf("\n\nCalculate the average...\n");

fprintf(fileptrOut, "Average of %i numbers = %f \n", count, total/(double)count);

printf("Average of %i numbers = %f \n\n", count, total/(double)count);

printf("Check also your %s file content\n", filenameOut);


if(fclose(fileptrIn) == 0)

printf("%s closed successfully\n", filenameIn);

if(fclose(fileptrOut) == 0)

printf("%s closed successfully\n", filenameOut);

return 0;



Output example:


Please enter an input filename (use path if needed):


Please enter an output filename (use path if needed):


Opening C:\input.txt for reading is OK.

Opening C:\output.txt for writing is OK.

The data:

23 12 33 10 4 6 44 31 7 50

The total: 220


Calculate the average...

Average of 10 numbers = 22.000000

Check also your C:\output.txt file content

C:\input.txt closed successfully

C:\output.txt closed successfully

Press any key to continue . . .


Try changing the integers in the input.txt and re-run the program, check the output.txt content.



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