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Chapter 6: Problem 18

Here is a code segment that reads input from infile.dat and sends output to outfile.dat. What changes are necessary to make the output go to the screen? (The input is still to come from infile. dat.) //Problem for Self Test. Copies three int numbers //between files. #include int main( ) { using namespace std; ifstream instream; ofstream outstream; instream.open("infile.dat"); outstream.open("outfile.dat"); int first, second, third; instream >> first >> second >> third; outstream << "The sum of the first 3" << endl << "numberss in infile.dat is " << endl << (first + second + third) << endl; instream.close( ); outstream.close( ); return 0; }

Short Answer

Expert verified
Answer: The program was modified to display the output on the screen by replacing the output stream 'outstream' (which was writing to "outfile.dat") with 'cout', the standard output stream for console output. In addition, the iostream header was added, and the lines related to creating, opening, and closing the 'ofstream' object 'outstream' were removed from the code.

Step by step solution

01

Identifying the Output Stream

Firstly, identify the output stream used in the program. Here, it is 'outstream' which is an object of 'ofstream' (output file stream).
02

Including the iostream Header

Since we need to use 'cout' for console output, make sure to include the iostream header at the beginning of the program. ``` #include ```
03

Replace 'outstream' with 'cout'

Replace 'outstream' in the code with 'cout', which is the standard output stream for console output.
04

Remove the Output File Stream

Since we are using 'cout' for output and are no longer using 'outstream', there is no need for the 'ofstream' object 'outstream' and its associated operations (such as opening and closing the output file stream). Remove the following lines from the code: ``` ofstream outstream; outstream.open("outfile.dat"); outstream.close(); ```
05

Modified Code

Here is the modified code that sends the output to the screen while still reading input from "infile.dat": ```cpp #include #include int main() { using namespace std; ifstream instream; instream.open("infile.dat"); int first, second, third; instream >> first >> second >> third; cout << "The sum of the first 3" << endl << "numbers in infile.dat is " << endl << (first + second + third) << endl; instream.close(); return 0; } ```

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Most popular questions from this chapter

Write the definition for a void function called text_to_screen that has one formal parameter called \(f\) ile_stream that is of type ifstream. The precondition and postcondition for the function are as follows: //Precondition: The stream file_stream has been connected //to a file with a call to the member function open. //Postcondition: The contents of the file connected to //file_stream have been copied to the screen character by //character, so that the screen output is the same as the //contents of the text in the file. //(This function does not close the file.)

Consider the following code (and assume that it is embedded in a com- plete and correct program and then run): char next; int count = 0; cout << "Enter a line of input:\n"; cin.get(next); while (next != '\n') { if ((count%2) == 0) cout << next; count++; cin.get(next); } If the dialogue begins as follows, what will be the next line of output? Enter a line of input: abcdef gh

Suppose you are writing a program that uses a stream called fin that will be connected to an input file and a stream called fout that will be connected to an output file. How do you declare \(f\) in and four? What include directive, if any, do you need to place in your program file?

What output will be sent to the file stuff.dat when the following lines are executed (assuming the lines are embedded in a complete and correct program with the proper include directives)? ofstream fout; fout.open("stuff.dat"); fout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; fout.setf(ios::showpos); fout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; fout.unsetf(ios::showpos); fout.setf(ios::left); fout << "*" << setw(5) << 123 << "*" << setw(5) << 123 << "*" << endl;

What output will be produced when the following lines are executed (assuming the lines are embedded in a complete and correct program with the proper include directives)? cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; cout.setf(ios::showpos); cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; cout.unsetf(ios::showpos); cout.setf(ios::left); cout << "*" << setw(5) << 123 << "*" << setw(5) << 123 << "*" << endl;
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