Answer:
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 <fstream>
#include<string>
#include <iostream>
#include <cstdlib> //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 ."<<endl;
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
