Implement the function fileSum. fileSum is passed in a name of a file. This function should open the file, sum all of the integers within this file, close the file, and then return the sum. If the file does not exist, this function should output an error message and then call the exit function to exit the program with an error value of 1.

The C+ + code is given below with appropriate comments for better understanding

Explanation:

/*C+ + program that prompts user to enter the name of input file (input. txt in this example) and print the sum of the values in the file to console. If file dosnot exist, then close the program * /

//header files

#include

#include

#include

#include / /needed for exit function

using namespace std;

//function prototype

int fileSum (string filename);

int main ()

{

string filename;

cout << "Enter the name of the input file: ";

cin >> filename;

cout << "Sum: " << fileSum (filename) << endl;

system ("pause");

return 0;

}

/*The function fileSum that takes the string filename and

count the sum of the values and returns the sum of the values*/

int fileSum (string filename)

{

//Create a ifstream object

ifstream fin;

//Open a file

fin. open (filename);

//Initialize sum to zero

int sum=0;

//Check if file exist

if (! fin)

{

cout<<"File does not exist."<
system ("pause");

exit (1);

}

else

{

int value;

//read file until end of file exist

while (fin>>value)

{

sum+=value;

}

}

return sum;

}//end of the fileSum