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I'm a student who just learned to use C++ for a few weeks. I write C++ code on Code:: Block and I am trying to run this code to learn about vector:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
vector<int> intVector;
for(int i = 0; i < 10; i++)
{
intVector.push_back(i+1);
}
cout << "Numbers in vector: ";
for(int i = 0; i < intVector.size(); i++)
{
cout << intVector[i] + " ";
}
}
But the output is really weird:
Numbers in vector: vector::_M_emplace_back_auxector::_M_emplace_back_auxctor::_M_emplace_back_auxtor::_M_emplace_back_auxor::_M_emplace_back_auxr::_M_emplace_back_aux::_M_emplace_back_aux:_M_emplace_back_aux_M_emplace_back_aux
Process returned 0 (0x0) execution time : 0.047 s
Press any key to continue.
Does anyone know how to fix this problem? Do I use vector in the wrong way?
Try changing the cout line like this:
cout << intVector[i] << " ";
What you're trying to do is add an int& and a string literal -- in some compilers it will emit a warning indicating for you that you're not getting what you intended for.
For example with Clang:
warning: adding '__gnu_cxx::__alloc_traits>::value_type' (aka 'int') to a string does not append to the string [-Wstring-plus-int]
cout << intVector[i] + " ";
~~~~~~~~~~~~~^~~~~
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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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I'm new to programming and i have problem with some items
i would appreciate any help
first i started initializing the vector as followed but i couldn't end the loop with Ctrl+Z
#include "stdafx.h"
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
vector <double> temps;
double temp;
cout << "Enter a sequence of tempreatures : " << "\n" ;
while (cin >> temp){
temps.push_back(temp);
}
double sum = 0;
for (int i = 0; i< temps.size(); ++i)
sum += temps[i];
cout << "Mean temprature : " << sum / temps.size() << "\n";
sort(temps.begin(), temps.end());
cout << "Median temprature : " << temps[temps.size() / 2];
then i changed the while into this format :
cout << "ENter a sequence of tempreatures ending in 1500 : " << "\n" ;
while (cin >> temp){
if (temp == 1500)
break;
temps.push_back(temp);
}
now i have this error
"vector subscript out of range"
apparently break does not work properly here
what should i do?
Your issue is in the check condition of for loop.
for (int i = 0; i, temps.size(); ++i)
sum += temps[i];
It should be
for (int i = 0; i < temps.size(); ++i)
i, temps.size() will evaluate and then ignore the part before , and are left with temps.size() as check condition which will always be greater than 0 if you push_back at least one element and your loop will never end.You might want to read how ,(comma) works.
If you switch to std::getline into a string instead of std::cin into a double, you can check whether the input is empty:
std::string input;
std::getline(std::cin, input);
while (!input.empty()){
temps.push_back(atof(input.c_str()));
std::getline(std::cin, input);
}
If you also fix the for-loop as mentioned by Gaurav Sehgal, it works fine (Enter all numbers then hit enter without any input).
If you are on windows then you have to do
CTRL + Z
If you are on Unix based(Linux/Mac) then you have to do
CTRL + D
This will give the end of file signal and you will be able to break the loop
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I have to write a function that goes through a string, finds any capital letters present and makes them lowercase. I decided to add a bit of code to show what letters were found and how many were found. Although on each compilation, the value of 'cnt' yields ridiculous results.
#include <iostream>
#include <vector>
using namespace std;
int upper(string s) {
int cnt;
vector<char> v{};
for (auto& i : s) {
if (isupper(i)) {
v.push_back(i);
i = tolower(i);
++cnt;
}
}
cout << "new string is '" << s << "'\n"
<< "number of capitals found is " << cnt << "\n"
<< "letters found were ";
for (auto l : v)
cout << l << " ";
return 0;
}
int main() {
string l = "This IS a TeSt";
upper(l);
}
I'm sure I must have done something wrong with the loop but whatever the problem is, I cannot find it.
The variable cnt is never initialized when used, change
int cnt;
to
int cnt = 0;
You failed to initialize the local variable cnt. Using an uninitialized value provokes undefined behavior, under which basically anything can happen.
Use int cnt=0; and please turn on all your compiler warnings.
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Whenever I try to run this program it returns an error saying:
no operator "<<" matches these operands
Also note that the program only runs into this problem in the getChoice() function.
#include <iostream>
#include "utilities.h"
using namespace std;
int getChoice(string inChoices[]){
int numOfChoices = sizeof(inChoices) / sizeof(inChoices[0]);
string x = inChoices[0];
string y = inChoices[1];
cout << x << endl << y << endl;
return numOfChoices;
}
int main()
{
string choices[2] = { "Happy Day", "Even Better Day" };
cout << utilities::getChoice(choices) << endl;
cout << endl << sizeof(choices) / sizeof(choices[0]) << endl;
}
You need also to include the string header:
#include <string>
You need to #include <string>
And your calculation of numOfChoices in getChoice() is wrong, since the parameter inChoices is actually a "pointer to string" instead of "array of strings".
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thanks for taking the time to help me out.
I'm really new with C++ and Xcode. I was working on a simple program to help me understand loops, so my goal was to make a simple "echo machine". This is my code:
string words;
int main()
{
do {
cout << "Enter text.";
cin >> words;
cout << "You entetered " << words << "!";
}
while (words != "goodbye");
return 0;
}
My result is nothing but lldb in parenthesis. I am very frustrated and can't find what I'm doing wrong anywhere. Please help and thank you so much.
Are you just missing the include directives for the standard headers you're using?
Try this:
#include <iostream>
#include <string>
using namespace std;
int main() {
string words;
do {
cout << "Enter text: ";
cin >> words;
cout << "You entered " << words << "!\n";
} while (words != "goodbye");
return 0;
}