I have to write a program that converts a decimal number between (1.0 - 99.99) into binary. My teacher said We can ONLY use the things we learned in class so far, witch include: Loops, input/output files, strings, if/else, cmath, and user defined functions. Ive started to program how to convert an integer to binary first before taking on the decimal. I am able to calculate the binary value but I am spitting out my binary in reverse order. So my teacher said to send the remainders(eg: bit values) to a file and read them as a string. Which is were I am now. Still with the same problem. How do I print these values from a string in reverse order?
My attempt so far:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
int number;
int remainder;
string bitValues;
ofstream outFile;
ifstream inFile;
//inFile.open("C:\\Users\\David\\Desktop\\BinaryIn.txt"); // pay no mind to this.
outFile.open("C:\\Users\\David\\Desktop\\BinaryOut.txt");
cout << "Enter a integer to be converted to binary: ";
cin >> number;
while(number != 0)
{
remainder = number % 2;
outFile << remainder << " "; // I send it to the outFile
number /= 2;
}
outFile.close(); // I close because I need to read from it now.
inFile.open("C:\\Users\\David\\Desktop\\BinaryOut.txt"); //I did this so I can read from the same outFile
getline(inFile, bitValues); //had to look up getline(), was not covered in class
// I just came up with this idea, is this Valid??????????
int posisiton = 10;
while(posisiton >= 0)
{
cout << bitValues[posisiton]; // I ever done something like this but It worked!
posisiton--;
}
int pause;
cin >> pause;
return 0;
}
Do you know how to write a recursive function? By doing the recursive call before outputting the remainder (as opposed to afterwards), you will get the effect you want.
1) Forget the file (I don't know how that was going to help. Maybe you misunderstood the teacher). Just write a simple function to reverse the string.
for(int i=0; i<bitValues.length()/2; ++i) {
char t = bitValues[i];
bitValues[i] = bitValues[bitValues.length()-1-i];
bitValues[str.length()-1-i] = t;
}
2) Or instead of using modulo, use a flag to get the bits in order the first time. This isn't code because it more directly relates to your homework, than a simple string reversal.
resize the string to be big enough to hold all the bits
set a mask to have a 1 in the 31st position
for each position in the string
use `&` with the mask to find if it's a one or zero
set the character depending on the bit
shift the mask right one.
Related
I am trying to run a code sorting the ages of Titanic survivors from a text file. It compiles fine, but the program terminates simply saying "segmentation fault" when I choose option B (option A is not written yet.)
Here is a small sample of the text file for reference.
29 1stClass TRUE
0.9 1stClass TRUE
2 1stClass FALSE
30 1stClass FALSE
I've isolated the error to the chunk where the file is processed (//actual processing), but I'm not sure what exactly is wrong.
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <fstream>
#include <ctype.h>
void sortSurvivors();
void sortAgesLiving();
int main()
{
char options;
std::cout << "Titanic Data \nOptions \nA) Display count of people who lived and died... \nB) Display count of people who lived by age... \nPlease select option (A-B)...";
std::cin >> options;
switch (options)
{
case 'A':
sortSurvivors();
break;
case 'B':
sortAgesLiving();
break;
}
}
void sortSurvivors()
{
}
void sortAgesLiving()
{
std::ifstream inputFile;
std::string filename = "TitanicData.txt";
std::string age;
std::string classBoat;
std::string survival;
bool survived;
int eldest = 0;
//pre-sort processing
while (inputFile >> age >> classBoat >> survival)
{
int ageConv = stoi(age);
//G is for the ghetto fix I am pulling here, because I recieve an error when using "TRUE" as a string
char gchar = 'G';
survival += gchar;
if (survival == "TRUEG")
{
survived = true;
}
else
{
survived = false;
}
if (eldest < ageConv)
{
eldest = ageConv;
}
}
//initialize vector
std::vector<int> survivorVector;
for (int i = 0; i < eldest; i++)
{
survivorVector.push_back(0);
}
inputFile.open(filename);
//actual processing (ERROR HERE)
if (inputFile)
{
while (inputFile >> age >> classBoat >> survival)
{
int ageConv = stoi(age);
if (survived = true)
{
survivorVector[ageConv] = survivorVector[ageConv] + 1;
}
for (int j = 0; j <= eldest; j++)
{
std::cout << j << "\t" << survivorVector[j] << "\n";
}
}
// Close the file.
inputFile.close();
}
else
{
std::cout << "I don't know what broke, but uhhhhhhhhhh oops.";
}
}
As per usual I'm sure it's something dumb I overlooked.
In sortAgesLiving(), you have forgotten to open the file before starting your pre-sort processing. As a consequence, your first reading loop will fail to read anything at all. Therefore eldest will stay 0.
You then construct a vector and populate it. But since the loop is based on eldest, the vector survivorVector will stay empty.
When you finally open the file and read it, the first line will be considered as a survivor since you accidentally overwrite the boolean with true (i.e. if (survived = true) instead of if (survived == true) or simply if (survived). You'll then try to access the vector out of bounds.
Even if you correct this error, at the first survivor you'll get again out of bounds. Accessing a vector out of bounds is UB and one of the many possible symptoms can be segmentation fault.
Miscellaneous advices (not related to your issues):
You have an ambiguous age of 0.9. Converting it to an int will cause it to be 0. Is this ok, or do you need to round this up?
If it's rounding up, you could make the age variable a double and read it directly without conversion. You could then convert it mathematically to an integer age rounding it up or truncating it, as needed. If you're sure to have only integers, you could make the variable an int and not worry at all.
It is unsafe to trust a value in a file to directly index a vector. What if between the two reading phases, an additional line would have been added by someone else to the file with a value higher than eldest ? What if the value read would be negative? Better always check that it's in an acceptable range before using a value as an index. It can save you hours of debugging and your customers some nightmares.
Finally, the two-phase read is not necessary: you could just read the age, and after having checked that it's positive and smaller than 150 years (quite optimistic), you could, if needed, resize your vector if the age is equal or larger than the current vector size. Why? Imagine you work one day for US census with files having millions of lines: the fewer passes over the file, the better ;-)
I have a simple program that converts decimal numbers to binary numbers. No errors come up when I run the program but I do get a single question mark. I should get a set of values like "00101" I am trying to use a function that returns a string as well. Here is my code,
#include <iostream>
using namespace std;
#include <string>
string convert(int num)
{
string binary;
int remainder;
while (num !=0 )
{
remainder = num % 2;
num = num / 2;
binary = remainder;
}
return binary;
}
int main()
{
int number;
string binaryNum;
cout << "Enter a Number:";
cin >> number;
binaryNum = convert(number);
cout << "This is your number in binary form:" << binaryNum << endl;
system("pause");
}
Any ideas?
Thanks for the help
There are several problems with this code. First, you are assigning the string binary using the = sign on the line binary = remainder. What you probably meant to write was binary += remainder, to append the remainder to the string.
The second problem is also on that line. Both string::operator= and string::operator+= have overloads that take a char. Those overloads are called, when you pass in an int. So the string is being set to the character whose ascii value is 0 or 1, thus the question mark character, which is not what you are looking for. You can use std::to_string to easily convert your int into a string. Or if you need any level of control over the formatting, you can use std::ostringstream as in this answer.
In other words, change binary = remainder; to binary += std::to_string(remainder).
Third problem: There is a return statement inside the while loop. The function will return after one iteration of the loop, no matter how large num is. Remove that return statement, so there is only the one at the very end of the convert function.
There is a basic problem with your code.
The while loop will iterate only once as you are returning a value.
You should concatenate binaryValue every time with remainder, and return it outside loop.
And I haven't checked the logic so do check it.
The first line contains an integer n (1 ≤ n ≤ 100). Each of the following n lines contains one word. All the words consist of lowercase Latin letters and possess the lengths of from 1 to 100 characters.
(Source: http://codeforces.com/problemset/problem/71/A)
How would you get input from the user given n? I tried using a while loop but it doesn't work:
#include <iostream>
using namespace std;
int main()
{
int n;
cin>>n;
int i;
while (i<=n) {
cin>>i ;
i++;
}
}
You probably meant to have something like:
#include <iostream>
int main() {
int n;
cin>>n;
int theInputNumbers[n];
for(int i = 0; i<n; ++i) {
cin >> theInputNumbers[i];
}
}
Your loop is really quite far off of what you need. What you wrote is extremely wrong such that I cannot provide advice other than to learn the basics of loops, variables, and input. The assistance you need is beyond the scope of a simple question/answer, you should consider buying a book and working through it cover to cover. Consider reading Programming Principles and Practice Using C++
Here is a working example of something approximating your question's requirements. I leave file input and output as an exercise up to you. I also make use of C++11's front and back std::string members. You would have to access via array index in older versions.
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main(){
int totalWords;
cin >> totalWords;
stringstream finalOutput;
for (int i = 0; i < totalWords; ++i){
string word;
cin >> word;
if (word.length() > 10){
finalOutput << word.front() << (word.length() - 2) << word.back();
}else{
finalOutput << word;
}
finalOutput << endl;
}
cout << endl << "_____________" << endl << "Output:" << endl;
cout << finalOutput.str() << endl;
}
With that said, let me give you some advice:
Name your variables meaningfully. "int i" in a for loop like I have above is a common idiom, the "i" stands for index. But typically you want to avoid using i for anything else. Instead of n, call it totalWords or something similar.
Also, ensure all variables are initialized before accessing them. When you first enter your while loop i has no defined value. This means it could contain anything, and, indeed, your program could do anything as it is undefined behavior.
And as an aside: Why are you reading into an integer i in your example? Why are you then incrementing it? What is the purpose of that? If you read in input from the user, they could type 0, then you increment by 1 setting it to 1... The next iteration maybe they'll type -1 and you'll increment it by 1 and set it to 0... Then they could type in 10001451 and you increment by 1 and set it to 10001452... Do you see the problem with the logic here?
It seems like you are trying to use i as a counter for the total number of iterations. If you are doing this, do not also read input into i from the user. That completely undermines the purpose. Use a separate variable as in my example.
I am fairly new to programming and have to create a program which reads the prompt: "I have 8 dollars to spend." It then needs to print out with each word on a separate line, and then if any of the strings is numeric, it needs to be divided by 2. Therefore it should end up printing out as:
I
have
4
dollars
to
spend.
I have managed to do everything, except finding the numeric value and dividing it by 2. So far I have this:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
string prompt;
string word;
cout << "Prompt: ";
getline(cin, prompt);
stringstream ss;
ss.str(prompt);
while (ss >> word)
{
cout << word << endl;
}
return 0;
}
After looking through various other posts, I cannot manage to get this to work. I'm assuming its an if/else statement within the while loop along the lines of, if numeric, set int num to num / 2 then cout << num << endl;, else cout << word << endl;, but I can't figure it out.
Thanks in advance.
You can use the stringstream class, which handles conversions between strings and other data types, to attempt to convert a given string to a number. If the attempt is successful, you know
The stringstream object allows you to treat a string as though it is a stream similar to cin or cout.
Incorporate this into your while loop, like so:
while (ss >> word)
{
int value = 0;
stringstream convert(word); //create a _stringstream_ from a string
//if *word* (and therefore *convert*) contains a numeric value,
//it can be read into an _int_
if(convert >> value) { //this will be false if the data in *convert* is not numeric
cout << value / 2 << endl;
}
else
cout << word << endl;
}
The strtol (C++11 version that works on std::string directly: std::stol) function is really good for testing whether a string holds a number, and if so, what the numeric value is.
Or you could continue using iostreams like you have been... try extracting a number (int or double variable), and if that fails, clear the error bit and read a string.
I dont have 50 rep so I cant comment, thats why I'm writing it as answer.
I think you can check it character by character, using Ascii value of each char, & if there are ascii values representing numbers between two spaces(two \n in this case as you've already seperated each word), then you have to divide the number by 2.
So I am currently learning C++ and decided to make a program that tests my skills I have learned so far. Now in my code I want to check if the value that the user enters is a double, if it is not a double I will put a if loop and ask them to reenter it. The problem I have is how do I go about checking what type of variable the user enters, ex- if a user enters a char or string, I can output an error message. Here is my code:
//cubes a user entered number
#include <iostream>
using namespace std;
double cube(double n); //function prototype
int main()
{
cout << "Enter the number you want to cube: "; //ask user to input number
double user;
cin >> user; //user entering the number
cout << "The cube of " << user << " is " << cube(user) << "." << endl; //displaying the cubed number
return 0;
}
double cube (double n) //function that cubes the number
{
return n*n*n; // cubing the number and returning it
}
Edit: I would have to say I just started and don't have the slightest of clue about your code, but I will check out your link. By the way, I haven't learned how to work with templates yet,I am learning about dealing with data, only Chapter 3 in my C++ Primer Plus 5th edition.
Safe C++ Way
You can define a function for this using std::istringstream:
#include <sstream>
bool is_double(std::string const& str) {
std::istringstream ss(str);
// always keep the scope of variables as close as possible. we see
// 'd' only within the following block.
{
double d;
ss >> d;
}
/* eat up trailing whitespace if there was a double read, and ensure
* there is no character left. the eof bit is set in the case that
* `std::ws` tried to read beyond the stream. */
return (ss && (ss >> std::ws).eof());
}
To assist you in figuring out what it does (some points are simplified):
Creation of a input-stringstream initialized with the string given
Reading a double value out of it using operator>>. This means skipping whitespace and trying to read a double.
If no double could be read, as in abc the stream sets the fail-bit. Note that cases like 3abc will succeed and will not set the fail-bit.
If the fail-bit is set, ss evaluates to a zero value, which means false.
If an double was read, we skip trailing whitespace. If we then are at the end of the stream (note that eof() will return true if we tried to read past the end. std::ws does exactly that), eof will return true. Note this check makes sure that 3abc will not pass our check.
If both cases, right and left of the && evaluate to true, we return true to the caller, signaling the given string is a double.
Similar, you check for int and other types. If you know how to work with templates, you know how to generalize this for other types as well. Incidentally, this is exactly what boost::lexical_cast provides to you. Check it out: http://www.boost.org/doc/libs/1_37_0/libs/conversion/lexical_cast.htm.
C Way One
This way has advantages (being fast) but also major disadvantages (can't generalized using a template, need to work with raw pointers):
#include <cstdlib>
#include <cctype>
bool is_double(std::string const& s) {
char * endptr;
std::strtod(s.c_str(), &endptr);
if(endptr != s.c_str()) // skip trailing whitespace
while(std::isspace(*endptr)) endptr++;
return (endptr != s.c_str() && *endptr == '\0');
}
strtod will set endptr to the last character processed. Which is in our case the terminating null character. If no conversion was performed, endptr is set to the value of the string given to strtod.
C Way Two
One might thing that std::sscanf does the trick. But it's easy to oversee something. Here is the correct way to do it:
#include <cstdio>
bool is_double(std::string const& s) {
int n;
double d;
return (std::sscanf(s.c_str(), "%lf %n", &d, &n) >= 1 &&
n == static_cast<int>(s.size()));
}
std::sscanf will return the items converted. Although the Standard specifies that %n is not included in that count, several sources contradict each other. It's the best to compare >= to get it right (see the manpage of sscanf). n will be set to the amount of the processed characters. It is compared to the size of the string. The space between the two format specifiers accounts for optional trailing whitespace.
Conclusion
If you are a beginner, read into std::stringstream and do it the C++ way. Best not mess with pointers until you feel good with the general concept of C++.
There is no suitable way to check if a string really contains a double within the standard library. You probably want to use Boost. The following solution is inspired by recipe 3.3 in C++ Cookbook:
#include <iostream>
#include <boost/lexical_cast.hpp>
using namespace std;
using namespace boost;
double cube(double n);
int main()
{
while(true)
{
cout << "Enter the number you want to cube: ";
string user;
cin >> user;
try
{
// The following instruction tries to parse a double from the 'user' string.
// If the parsing fails, it raises an exception of type bad_lexical_cast.
// If an exception is raised within a try{ } block, the execution proceeds
// with one of the following catch() blocks
double d = lexical_cast <double> (user);
cout << "The cube of " << d << " is " << cube(d) << "." << endl;
break;
}
catch(bad_lexical_cast &e)
{
// This code is executed if the lexical_cast raised an exception; We
// put an error message and continue with the loop
cout << "The inserted string was not a valid double!" << endl;
}
}
return 0;
}
double cube (double n)
{
return n*n*n;
}
sscanf can do what you want; it returns the number of arguments properly processed. This should get you started:
//cubes a user entered number
#include <iostream>
#include <cstdio>
using namespace std;
double cube(double n); //function prototype
int main()
{
cout << "Enter the number you want to cube: "; //ask user to input number
string user;
cin >> user; //user entering the number
// Convert the number to a double.
double value;
if(sscanf(user.c_str(), "%lf", &value) != 1)
{
cout << "Bad! " << user << " isn't a number!" << endl;
return 1;
}
cout << "The cube of " << user << " is " << cube(user) << "." << endl; //displaying the cubed number
return 0;
}
double cube (double n) //function that cubes the number
{
return n*n*n; // cubing the number and returning it
}
Other methods posted in other answers have their advantages and disadvantages. This one has issues with trailing characters and isn't "C++"-y.
I would have to say I just started and don't have the slightest of clue about your code, but I will check out your link. By the way, I haven't learned how to work with templates yet,I am learning about dealing with data, only Chapter 3 in my C++ Primer Plus 5th edition.
You can fall back on C and use strtod
You program reads in a string and then passes it to a function that attempts to convert the string into double.
bool is_double(const char* strIn, double& dblOut) {
char* lastConvert = NULL;
double d = strtod(strIn, &lastConvert);
if(lastConvert == strIn){
return false;
} else {
dblOut = d;
return true;
}
}