Need Help Adding something to my code

[gordon2013]

I have the following code (shown below) compiling correctly and I'm able to run it. The only thing I need to add is logic so that if there is no input data file in the directory, to display a message "Error Opening File". How can I do this?

This code looks for an input_data.txt file, then it calculates something and writes to another file called output_data.txt file.

int main ()
{
	FILE *fptr1;
	FILE *fptr2;
	char fName[20];
	char lName[20];
	char buf[100];
	char letterGrade;
	int final_score;
	int count;
	int quiz1, quiz2, quiz3, quiz4, mid, final;


	fptr1 = fopen("input_data.txt","r");
//display the results
	fptr2 = fopen("output_data.txt","w");
//reading using fscanf


	while(fscanf(fptr1,"%s %[^ \t\n\r\v\f,]%*c %d, %d, %d, %d, %d, %d", fName,lName,&quiz1,&quiz2,&quiz3,&quiz4,&mid,&final) != EOF)
	{
//determine final_score calculation 
		final_score = quiz1*.10 + quiz2*.10 + quiz3*.10 + quiz4*.10 + mid*.25 + final*.35; 
		printf("%d", final_score); 


//determine letter grade based on final_score
		if (final_score >= 90) 
			letterGrade = 'A'; 
		else if (final_score >= 80 && final_score < 90)
			letterGrade = 'B'; 
		else if (final_score >= 70 && final_score < 80) 
			letterGrade = 'C'; 
		else if (final_score >= 60 && final_score < 70) 
			letterGrade = 'D'; 
else
			letterGrade = 'F'; 


//following code will output the file 
//and move on to the second student
		if(fptr2) 
		{
			fprintf(fptr2, "%s %s     :%c\n", fName, lName, letterGrade); 
			fflush(fptr2); 
		}
	}
	fclose(fptr1); 
	fclose(fptr2); 
}

[AndiPersti]

Please don't ask the same question in two threads. Stick to one.

Bye, Andreas