I am learning std::string and I want to :
Input string
Every second letter make Uppercase
Output new string
#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int main()
{
string myStr;
getline(cin,myStr);
if (myStr.begin() != myStr.end())
{
for (auto it = myStr.begin(); it != myStr.end() ; it += 2)
*it = toupper(*it);
}
cout << myStr;
system("pause");
return 0;
}
But after input I am getting error here:
it += 2 leads you out of bounds, if the loop ending condition is it != myStr.end(). Thus dereferencing
*it = toupper(*it);
is undefined behavior.
it += 2 will never give you an exact iterator value of myStr.end() as you have for your loops termination condition.
As for your comment:
So how can i fix it ?
Just keep it simple and understandable, like e.g. using something like
for (size_t i = 0; i < myStr.length() ; ++i) {
if(i % 2) { // Every second letter ...
myStr[i] = toupper(myStr[i]);
}
}
Related
C++
Hi, I'm new to coding, I wanted to know why "str.replace" didn't work in the "for(char& i : str)" loop but it did in the "for (int i = 0; i <= str.length(); i++)" loop.
#include <iostream>
#include <string>
using namespace std;
int main()
{
string str = "aNo more 'a'";
int sum;
for (char& i : str){
if (i == 'a'){
sum += 1;
}
}
cout << str << " " << sum;
return 0;
}
Output: "aNo more 'a' 2"
This code seems to work fine.
#include <iostream>
#include <string>
using namespace std;
int main()
{
string str = "aNo more 'a'";
int sum;
for (char& i : str){
if (i == 'a'){
str.replace(i,1,"");
}
}
cout << str << endl;
return 0;
}
Error: Terminate called after throwing an instance of 'std::out_of_range'
what(): basic_string::replace: __pos (which is 97) > this->size() (which is 12)
#include <iostream>
#include <string>
using namespace std;
int main()
{
string str = "aNo more 'a'";
int sum;
for (int i = 0; i <= str.length(); i++){
if (str[i] == 'a'){
str.replace(i,1,"");
}
}
cout << str << endl;
return 0;
}
Output: "No more '' "
This code works fine because it's not running into the range error listed above. I don't know why that is. Can someone help me understand why the "for(char& i : str)" doesn't work?
A range based for-loop like this:
for (char& i : str) {
if (i == 'a') {
str.replace(i, 1, "");
}
}
Is roughly the same as:
for(auto it = std::begin(str), end = std::end(str); it != end; ++it) {
if (*it == 'a') {
str.replace(*it, 1, "");
}
}
It'll use the character value (i in your code or *it in my loop) as the position in the string where to start replacing. The character 'a' has the ASCII value 97 which explains the exception you get since 97 is clearly out of bounds.
If you change the length of str inside the loop, end will be invalidated and it will run out of bounds.
You may find using std::erase(std::string) easier. This will remove all 'a's from str:
std::erase(str, 'a');
When using a range-for in C++, the current element (i in this case) is not actually an iterator but rather is the element itself, thus i would have the value of the current element. Here you've declared i as char& meaning it is a reference to a character in the collection.
When you passed i to std::string::replace() it expected the first argument to be a value indicating the position you want to replace at. Because char is a smaller integral type it gets promoted to the std::string::size_type ::replace() expects for its first argument, for example 'a' would become 97. Because this is technically valid to request it tries to replace at that position but because 97 is out of the strings range it throws an exception, as it should.
It is considered bad practice to try and modify a container directly in a for loop, particularly a range-for loop as the end of the container becomes invalidated if reallocation occurs, which erasure and replacement often do.
Instead, to achieve the desired outcome, one can utilize a combination of the algorithms std::remove and std::string::erase or if you can use C++20 std::erase_if
std::string str = "aNo more 'a'";
auto end_no_as = std::remove(std::begin(str), std::end(str), 'a');
str.erase(end_no_as, std::end(str));
/// or
std::erase_if(str, [](char& c){ return c == 'a'; });
Godbolt Demo
Will some one explain or make a program in c++ of this for me? Got assignment but don't know how to do it.
Question: You are given a set of strings which contain only as and bs, your program should be able to check whether each string has the same number of as and bs in it or not.
e.g. The program will respond true if it get {ab, aabb, aaabbbb, bbbaaa} and say false when it gets {aab, bbba, aaabbbb}
Solve it using stack
#include <iostream>
#include <string>
#include <stack>
#include <algorithm>
using namespace std;
int count1 = 0;
int count2 = 0;
bool isInLanguageL (string w);
int main()
{
string input;
cout << "Input any string; ";
getline(cin,input);
if (input.length() % 2 != 0)
cout <<"Pattern entered does not match the language ";
else
isInLanguageL(input);
return 0;
}
bool isInLanguageL (string w)
{
stack<string> word1, word2;
string a, b;
for (unsigned i = 0; i < w.length()/2; i++)
{
a = w.at(i);
word1.push(a);
}
reverse(w.begin(), w.end());
for (unsigned i = 0; i < w.length()/2; i++)
{
b = w.at(i);
word2.push(b);
}
while(!word1.empty() && !word2.empty())
{
word1.pop();
count1 = count1++;
word2.pop();
count2 = count2++;
}
if(count1 == count2)
return true;
else
return false;
}
This solution is using stack, please refer to the comments written in the code. If you have any doubt you can comment them.
Code:
#include <iostream>
#include <stack>
#include <string>
using namespace std;
void checkString(string s) {
if (s.size() % 2 != 0) {
cout << "Doesn't satisfy the conditon\n";
return;
}
stack<char> st;
int n = s.size();
for (int i = 0; i < n; ++i) {
/*
case - 1 : If the stack is empty you can directly push the current character into the stack
case - 2 : If there are elements present in the stack, then if the current character is equal to the top character on the stack then we can push the current character
beacuse we didn't find any new character to match them.
*/
if (st.empty() || (st.top() == s[i])) {
st.push(s[i]);
}
/*
case-3 : If the stack is not emtpy and current character is different from the top character on the stack then we found a match like a-b (OR) b-a, so then we will
remove the top element from the stack and move to next character of the string
*/
else if (st.top() != s[i]) {
st.pop();
}
}
/*
case - 1 : After iterating through all the characters in the string, if we find the stack is emtpy then we can say all characters are not matched
case - 2 : If stack is emtpy, then that means all the characters are matched.
*/
(st.empty()) ? (cout << "Yes, satisfies the conditon\n") : (cout << "Doesn't satisfy the conditon\n");
}
int main() {
string s = "";
cin >> s;
checkString(s);
return 0;
}
Your solution has a number of mistakes that you should probably solve by using a debugger. Here's a reference.
This solution doesn't use a stack as you asked for, but you can write this function that uses algorithms to solve your problem:
namespace rs = std::ranges;
bool all_equal_as_and_bs(auto const & strings)
{
return rs::all_of(strings, [](auto const & string)
{
return rs::count(string, 'a') == rs::count(string, 'b');
});
}
And use it like this:
all_equal_as_and_bs(std::vector<std::string>{"ab", "aabb", "aaabbb", "bbbaaa"}); // true
all_equal_as_and_bs(std::vector<std::string>{"aab", "bba", "aaabbbb", "bbbaaa"}); // false
I have a small program that prints out the capital form of each letter of a word, but I get the error signed/unsigned mismatch when I compile it because I'm passing a cstring as a normal string in this program. How do I pass it correctly so that I can still use text.length()? Here is the error that I get "Tester.cpp(22,23): warning C4018: '<': signed/unsigned mismatch". It's at for (int i = 0; i < text.length(); i++)
#include <iostream>
using namespace std;
string capitalizeFirstLetter(string text);
int main() {
char sentence[100];
for ( ; ; )
{
cin.getline(sentence, 100);
if (sentence != "0")
capitalizeFirstLetter(sentence);
}
return 0;
}
string capitalizeFirstLetter(string text) {
for (int i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
cout << text;
return text;
}
The simplest way to handle passing sentence as a string is to enclose it in a braced set, to provide direct initialization to the parameter std::string text eg..
for ( ; ; )
{
std::cin.getline(sentence, 100);
if (*sentence)
capitalizeFirstLetter({sentence});
}
This allows the character string sentence to be used as the Direct initialization to initialize std::string text in your capitalizeFirstLetter() function:
std::string capitalizeFirstLetter (std::string text) {
for (size_t i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
std::cout << text;
return text;
}
Your complete code, after reading Why is “using namespace std;” considered bad practice?, would then be:
#include <iostream>
std::string capitalizeFirstLetter (std::string text) {
for (size_t i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
std::cout << text;
return text;
}
int main (void) {
char sentence[100];
for ( ; ; )
{
std::cin.getline(sentence, 100);
if (*sentence)
capitalizeFirstLetter({sentence});
}
return 0;
}
(note: dereferencing sentence provides the first character which is then confirmed as something other than the nul-terminating character (ASCII 0))
A Better CapitalizeFirstLetter()
A slightly easier way to approach capitalization is to include <cctype> and an int to hold the last character read. Then the logic simply loops over each character and if the first character is an alpha-character, then capitalize it, otherwise only capitalize the letter when the current character is an alpha-character and the last character was whitespace, e.g.
std::string capitalizeFirstLetter (std::string text)
{
int last = 0
for (auto& c : text)
{
if (isalpha(c))
{
if (!i || isspace (last))
c = toupper(c);
}
last = c;
}
std::cout << text;
return text;
}
(note: the use of a range-based for loop above)
Either way works.
The error is not generating because of you passing a cstring as a normal string to the function but it is due to the fact that you are trying to compare c style string using != operator in the statement
if (sentence != "0")
capitalizeFirstLetter(sentence);
try using strcmp() for that
Several things bugging me here.
First off, don't use using namespace std, it's "ok" in this case, but don't get used to it, it can cause quite some trouble.
See Why is “using namespace std;” considered bad practice?
Next thing is, just use std::string instead of cstrings here, it's easier to write and to read and doesn't produce any measurable performance loss or something. And it's harder to produce bugs this way.
So just use
std::string sentence;
and
getline(std::cin, sentence);
And why do you handle the output inside the function that transforms your string? Just let the main print the transformed string.
So your main could look like this:
int main() {
std::string sentence;
while(true)
{
getline(std::cin, sentence);
auto capitalized = capitalizeFirstLetter(sentence);
std::cout << capitalized;
}
return 0;
}
PS: the 'error' you get is a warning, because you compare int i with text.length() which is of type size_t aka unsigned int or unsigned long int.
Problems with your code :
if (sentence != "0") : illegal comparison. If you want to break on getting 0 as input then try using strcmp (include <cstring>) as if (strcmp(sentence, "0"). (Note that strcmp returns 0 when two strings are equal.) Or simply do if (!(sentence[0] == '0' and sentence[1] == 0)). Moreover this condition should be accompanied with else break; to prevent the for loop from running forever.
for (int i = 0; i < text.length(); i++) : generates warning because of comparison between signed and unsigned types. Change data-type of i to string::size_type to prevent the warning.
<string> (for std::string) and <cctype> (for std::toupper) were not included.
Thanks to #john for pointing this out. Your code has undefined behaviour if last character of a string is a space. Add a check if i is still less than text.length() or not before using text[i].
Another case of error is when an space is there after 0. Move getline to condition of for to fix this. Now there will be no need to input a 0 to terminate program. Moreover, I recommend using while loop for this instead of for.
You may also need to print a newline to separate sentences. Moreover, I would prefer printing the modified sentence in the main() function using the returned string from capitalizeFirstLetter.
It doesn't matter much in short (beginner-level) codes, but avoid acquiring the habit of putting using namespace std; on the top of every code you write. Refer this.
Fixed code :
#include <cctype>
#include <cstring>
#include <iostream>
#include <string>
using namespace std;
string capitalizeFirstLetter(string text);
int main() {
char sentence[100];
while (cin.getline(sentence, 100))
cout << capitalizeFirstLetter(sentence) << '\n';
}
string capitalizeFirstLetter(string text) {
for (string::size_type i = 0; i < text.length(); i++) {
if (i == 0)
text[i] = toupper(text[i]);
if (text[i] == ' ')
if (++i < text.length())
text[i] = toupper(text[i]);
}
return text;
}
Sample Run :
Input :
hello world
foo bar
Output :
Hello World
Foo Bar
My Version (Requires C++20) :
#include <cctype>
#include <iostream>
#include <string>
auto capitalizeFirstLetter(std::string text) {
for (bool newWord = true; auto &&i : text) {
i = newWord ? std::toupper(i) : i;
newWord = std::isspace(i);
}
return text;
}
int main() {
std::string sentence;
while (std::getline(std::cin, sentence))
std::cout << capitalizeFirstLetter(sentence) << std::endl;
}
Sample Run
I am creating a program that scans user input for words that are listed in an array. The find() function seems like it'll work, but I can't find anything showing how to implement it for what I want to do. I'm pretty new to programming (obviously).
#include <iostream>
#include <time.h>
#include <stdlib.h>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
string subj [5]={"I","He","She","We","They"};
string verb [5]={" like"," hate"," sacrifice"," smell"," eat"};
string obj [5]={" bacon","s cats","s bagels","s children","s cops"};
string greeting [5]={"How are you","How's it going","Sup dude","Hey","Hello"};
string negvibe [4]={"bad","terrible","lousy","meh"};
string userfeeling;
int main()
{
srand(time(0));
int rando = rand() %5;//generates a random number between 0 and 4
int rando1 = rand() %5;
int rando2 = rand() %5;
cout << greeting [rando1] << "." << endl;
getline(std::cin,userfeeling);
if .... // What has to be done here?
find(negvibe, negvibe + 4, userfeeling) != negvibe + 4);
// Something like that?
// then ...
{
cout << subj[rando] << verb[rando1] << obj[rando2] <<"." <<endl;
}
return 0;
}
To make find work properly you should user iterators like so
if(find(std::begin(negvibe), std::end(negvibe), userfeeling) != std::end(negvibe)){
//code you want to happen if your word is found
}
Also in your current code, the if statement doesnt actually do anything since you end it with a semicolon and not {} or leave it blank if its one line. You can see an example of the if statement as well
Below is a link to find and iterators
http://www.cplusplus.com/reference/algorithm/find/
That find function will find some element of the negvibe array that is equal to userfeeling. If you are checking whether any element of negvibe is a substring of userfeeling, you should loop through negvibe and use the std::string::find method.
bool found_negvibe = false;
for (int i = 0; i < sizeof(negvibe) / sizeof(*negvibe); i++) {
found_negvibe = found_negvibe || userfeeling.find(negvibe[i]) != string::npos;
}
Also, you don't need to specify the size of the negvibe array, you can write this:
string negvibe[] = {"bad","terrible","lousy","meh"};
One more thing, you might prefer to use a std::vector over an array, if only because c++'s faculties for getting the size of a vector are slightly more succinct than those for getting the size of an array.
vector negvibe = {"bad","terrible","lousy","meh"};
bool found_negvibe = false;
for (int i = 0; i < negvibe.size(); i++) {
found_negvibe = found_negvibe || userfeeling.find(negvibe[i]) != string::npos;
}
I am trying to code a program where it takes a program as an input and prints out all the comments written in that program in a separate line.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
for(i=0;str[i]!='/' && str[i+1] !='/';i++);
//cout<<i;
for(i;str[i]!='\n';i++) {
// cout<<i;
cout<<str[i];
}
cout<<endl;
}
return 0;
}
I am getting a segmentation fault in this code and I can't understand why. This is part of a code of a problem in hackerrank https://www.hackerrank.com/challenges/ide-identifying-comments/copy-from/12957153
As commented in your question your code is wrong. First you are treating std::string object, returned by getline, as character array. Secondly your for loops never end if there is no // or \n found in input string. So obviously it will crash. Below is the modified code.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
size_t len = str.length();
const char *cstr = str.c_str();
for(i=0; (cstr[i]!='/' && cstr[i+1] !='/' && i < len); i++)
//cout<<i;
for(; cstr[i]!='\n' && i < len;i++) {
// cout<<i;
cout<<cstr[i];
}
cout<<endl;
}
return 0;
}
int main() {
while(getline(cin,str)) {
int i, len = str.size();
//always make sure that you are not accessing
//contents after your string has ended
for(i=0; i < (len - 1) && !(str[i] == '/' && str[i+1] == '/'); i++);
//note that i here might be the last alphabet
//if there's no comment
if(i < len && str[i] != '/')
i++;
//checking if str[i] != '\n' is not a good idea
//as c++ stl strings are not temrinated by '\n'
if(i < len) {
for(; i < len; i++)
cout << str[i];
cout << endl;
}
}
return 0;
}
Also note that both of the following codes won't terminate at the 4th character, c++ stl strings are not terminated by these characters.
string str = "hahahaha";
str[4] = '\n';
cout << str;
str[4] = '\0';
cout << str;
This is much easier to write and probably much faster than the other solutions to date.
#include <iostream>
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
size_t loc = str.find("//");
if (loc != str.npos)
{
std::cout << str.substr(loc + 2)<< std::endl;
}
}
return 0;
}
It is also wrong.
Here is a nice, clean, and simple state machine version. Also pretty close to worst-case for speed. Thing is it's closest to being right, even though it is also wrong.
#include <iostream>
enum states
{
seeking1,
seeking2,
comment
};
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
states state = seeking1;
for (char ch:str)
{
switch (state)
{
case seeking1:
if (ch == '/')
{
state = seeking2;
}
break;
case seeking2:
if (ch == '/')
{
state = comment;
}
else
{
state = seeking1;
}
break;
case comment:
std::cout << ch;
break;
}
}
if (state == comment)
{
std::cout << std::endl;
}
}
return 0;
}
Why are these approaches all wrong? Consider the line
cout << "Hi there! I am \\Not A Comment!" << endl;`
You can't just look at the \\, you also need the context. This is why the state machine above is the better option. It can be modified to handle, at the very least, states for handling strings and block comments.