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My output file is supposed to show to answer to the function it calls on. The program runs fine, however it is not displaying the text in the "prime" function. the output file, when checked, only displays 1's. I believe this is due to the fact that its declared as a bool function, and set to return true. However, how would I get this code to return the solution in Prime to the output file?
#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
using namespace std;
bool prime(int);
int main()
{
int reader;
ifstream Infile;
Infile.open("numlist.txt");
ofstream outputFile;
outputFile.open("theoutput.txt");
while (Infile >> reader)
{
outputFile << prime(reader) <<endl;
}
Infile.close();
outputFile.close();
}
bool prime(int p)
{
if (p % 2 == 0)
cout << "\n" << p << "\n Is not a prime number";
else if (p % 2 != 0)
cout << "\n" << p << "\n is a prime number";
return true;
}
No errors, however the output file is only showing 1's.
This is happening because in your prime() function, all the output is going to cout and not into outputFile. The prime() function returns a bool which is what is sent to outputFile.
If you'd like to have output of the function go to outputFile, you can either pass outputFile as a parameter and use that instead of cout or make it global.
A few more comments on your code: you don't need the full else if (p % 2 != 0) in the else statement. You can just use else, because p % 2 is either 0 or it's not, there's no other option.
Also, strongly recommend using braces around if statements, even if they are just a single line.
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I have simplified the code to get rid of unrelated objects. This is my code:
#include <iostream>
#include <fstream>
using namespace std;
fstream asdf;
int input;
void import_image(){
asdf.seekg(0);
char character;
for(int k = 0; k < 40; k++){
asdf.get(character);
input = (unsigned int)(unsigned char)character;
}
}
void print_hello_world(){
for(int rows; rows <= 27; rows++){
cout << "hello world" << endl;
}
cout << "goodbye.";
}
int main(){
asdf.open("abc.txt", ios::binary | ios::in);
cout << asdf.is_open() << endl;
import_image();
//cout << endl;
print_hello_world();
return 0;
}
Running this code results only in
1
goodbye.
--------------------------------
Process exited after 0.1511 seconds with return value 0
however removing double slash (simply adding cout << endl;) fixes everything. I have no idea why it happens and would like to now why is it so. I know that variable "rows" has no value, but why does printing a new line fix everything?
The new "endl"
is a great sign
that what you see,
is called "UB".
Your program has Undefined Behavior (UB) because your int rows that you use for the loop iterations is uninitialized.
By UB definition anything may happen. Activate all (sane) compiler warnings to find errors like this earlier in your development process.
Undefined behavior yield working programs by completely random changes (for example the addition of std::endl) but in the end it's undefined behavior.
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int main()
inFile.get(file);
while(inFile) {
inFile.get(file);
cout << file;
if(inFile.fail()) {
break;
}
if(inFile) {
++charNum;
}
if(inFile && c =='<') {
++comNum;
}
The values keep outputting 1, and its not actually counting the amount of < in the file. If I put inFile >> c, it makes my file a bunch of gibberish. What is the best way to count a certain amount of characters within a file, that is being opened by the user? Thank you.
You can rely on algorithms provided by the Standard Library.
#include <algorithm>
#include <fstream>
#include <iostream>
int main(int argc, char* argv[]) {
std::ifstream fp(argv[1]);
const auto count = std::count(std::istreambuf_iterator<char>{fp},
std::istreambuf_iterator<char>{}, '<');
std::cout << "count: " << count << "\n";
}
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My while loop is not working. The code runs correctly on the Codecademy website compiler. I then compile it with Visual Studio, run it from the Command prompt and input a number. The program stops prematurely even if the number is the correct one.
#include <cstdlib>
#include <iostream>
int main() {
int answer = 8;
int guess;
int tries;
std::cout << "I have a number between 1-10.\n";
std::cout << "Please guess it: ";
std::cin >> guess;
while (guess != 8 && tries < 50) {
std::cout << "Wrong guess, try again: ";
std::cin >> guess;
tries++;
}
if (guess == 8) {
std::cout << "You got it!\n";
}
}
As #rsjaffe and #Ken White have said in the comments, the tries variable is unitiailized, meaning that the location in memory that the variable is pointing to is "junk" (left over memory). Try to give it an initial value, like this:
int tries = 0;
which will instantiate and initialize the tries variable.
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I am a newbie in C++, I started to learn coding in C++ two weeks ago. Why does my code below always give me result 0 when I build and run? Please help
# include <iostream>
# include <string>
using namespace std;
int main ()
{
int input = 1;
cout << "input your number : \n";
cin >> input;
int faktorial = 1;
for(int i=1;i<=input;i++)
{
faktorial = faktorial * i;
}
cout << "factorial value from number " << input << " is " << faktorial << endl;
}
Your code works: https://ideone.com/CYFaxo
I suspect your problem is, you are looking at program exit code. When you don't return any value from main, program exit code is 0 (this is special case, and only non-void function where you may leave the return statement out), which conventionally means success (non-zero exit code usually indicates some kind of error, by convention).
Try to find the program output from your IDE, it should have the correct printout.
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What have I done wrong with the following code?
#include <iostream>
using namespace std;
main ()
{
int a;
int b;
int sum;
cout << "Enter first number \n";
cin >> a;
cout << "Enter second number \n";
cin >> b;
sum = a+b;
cout << "The sum of both numbers is" << sum << endl;
return 0;
}
Does the editor you are using tells errors, so the code is not executing? Or som exception rises? Or it is executing but nothing is shown? Please specify your problem accurately.
Anyway, you must use
int main ()
instead of
main()
Notice that your code returns a value. The last line of you code is:
return 0;
Thus, you must specify an int return type.
Check your initial lines with this.
#include <iostream>
using namespace std;
int main ()
{