#include<iostream>
#include<string>
using namespace std;
int main(){
string str;
cout << "Enter a string: ";
getline(cin, str);
int length = str.length();
string temp;
int k = 0;
for(int i = length-1; i>=0; i--){
temp[++k] = str[i];
}
cout<<temp;
return 0;
}
Actually, i want to find out whether the given string is a palindrome or not, so i am storing the first string in second one in reverse order , and then will ultimately check whether they are equal or not, but i am unable to print out even the result of temp string
You defined an empty object of the type std::string
string temp;
So you may not use the subscript operator with the empty object in the loop.
int k = 0;
for(int i = length-1; i>=0; i--){
temp[++k] = str[i];
}
Using your approach you could just write
string temp( str.rbegin(), str.rend() );
without using a loop.
However to check whether a string is a palindrome there is no need to create an intermediate string.
You could do it in a loop the following way.
std::string::size_type i = 0;
for ( auto n = str.length(); i < n / 2 && str[i] == str[n - i - 1]; )
{
++i;
}
if ( i == str.length() /2 ) std::cout << str << " is a palindrome\n";
Or without the loop and defining one more variable you could write
if ( str == std::string( str.rbegin(), str.rend() ) )
{
std::cout << str << " is a palindrome\n";
}
Related
I don't know how to use the find() function to check if a string contains a substring, then the program should print out all Words, and "Contains" if Sentence contains at least one of them. Can anyone help me out? My usage of find() sets A always to true. Thanks for help
#include <iostream>
#include <string>
using namespace std;
string Words, Sentence, buf;
int i, n, j = 0;
string arr[20];
bool A;
int main() {
cout << "Words separated by slashes";
cin >> Words;
cout << "Sentence";
cin >> Sentence;
for (i = 0; i <= Words.length(); i++)
{
if (Words[i] != '/')
{
buf = buf + Words[i];
}
else
{
arr[n] = buf;
n = n + 1;
buf = "";
}
}
for (j = 0; j <= n; j++)
{
cout << arr[j] << "\n";
if (Sentence.find(arr[j]) != string::npos)
{
A = true;
}
}
if (A == true)
{
cout << "Contains.";
}
else
{
enter code herecout << "Does not contain.";
}
}
There are a few bugs and issues in this code I think, but the biggest is the for loops all go too far by one.
for (i = 0; i <= Words.length(); i++)
and
for (j = 0; j <= n; j++)
should be
for (i = 0; i < Words.length(); i++)
and
for (j = 0; j < n; j++)
The valid indexes for a string, vector or array are zero upto but not including the size of the string, vector or array.
This mistake causes the bug that you see. Suppose you have two words in arr, e.g. arr = { "stack", "overflow", "", "", ... } . Because you go around the for loop one too many times you end up searching for arr[2] which equals "". This search always succeeds because every string contains the empty string. And so you always set A to true.
so I wrote this code to reverse one of the names based on the user option the idea is to use another function to reverse and to use pointers but after trying all I could think of my code return the same name not changed the best I could do was changing the first letter of the name to a weird sign.
#include <iostream>
using namespace std;
void reverse(char* A) {
int count = 0;
char temp[10];
for (int i = 0; A[i] != NULL; i++)
count++;
for (int i = 0; A[i] != NULL; i++) {
temp[count]=A[i];
count--;
}
for (int i = 0; A[i] != NULL; i++) {
A[i] = temp[i];
}
}
int main(){
int x= 0;
int index;
char Name_list[5][10];
cout << "please enter the names of the student " << endl;
for (int i = 0; i < 5; i++) {
cin >> Name_list[i];
for (int j = 0; Name_list[i][j] != NULL; j++) {
x++;
}
while (x > 10)
{
x = 0;
cout << "you have entered more then the allowed number of characters per name enter another name " << endl;
cin >> Name_list[i];
for (int j = 0; Name_list[i][j] != NULL; j++) {
x++;
}
}
x = 0;
}
for (int i = 0; i < 5; i++) {
cout << Name_list[i] << endl;
}
cout << "please enter the index of the name you want to reverse" << endl;
cin >> index;
while (index>4||index <0)
{
cout << "you entered incorrect index please enter a number from 0 to 4 " << endl;
}
reverse(Name_list[index]);
for (int i = 0; i < 5; i++) {
cout << Name_list[i] << endl;
}
system("pause");
}
For starters such a function should return a pointer to the result string. That is it should be declared like
char * reverse( char *s );
Note: do not use variable names consisting from upper case letters.
The type int can be not large enough to store length of a string. Instead use the type size_t.
char * reverse( char *s )
{
size_t count = 0;
//...
It is totally unclear why there is present an array with the number of elements equal to the magic number 10
char temp[10];
To reverse a string there is no need to declare an auxiliary array. Such an approach is principally wrong.
In this for loop
for (int i = 0; A[i] != NULL; i++)
there is compared an object of the type char with the pointer NULL. The compiler should issue a message for such a wrong comparison. It seems you mean
for (int i = 0; A[i] != '\0'; i++)
In any case the introduced variable i in this first for loop is redundant because you already has the variable count.
As you have the array temp with the fixed size equal to 10 then the both loops after the first loop can invoke undefined behavior even if the length of the source string is equal exactly to 10.
And the result string is not zero terminated.
The function can look the following way.
char * reverse( char *s )
{
size_t count = 0;
while ( s[count] ) ++count;
for ( size_t i = 0; i < count / 2; i++ )
{
char c = s[i];
s[i] = s[count - i - 1];
s[count - i - 1] = c;
}
return s;
}
Or using standard functions you could write the function reverse the following way
#include <utility>
#include <cstring>
//...
char * reverse( char *s )
{
for ( size_t i = 0, n = std::strlen( s ); i < n / 2; i++ )
{
std::swap( s[i], s[n-i-1] );
}
return s;
}
Pay attention to that there is the standard algorithm std::reverse. Using it you could reverse a string the following way
std::reverse( s, s + std::strlen( s ) );
for (int i = 0; A[i] != NULL; i++) {
temp[count]=A[i];
count--;
}
If i goes up from 0 to 5, count goes down from 6 to 1.
Ok, a few things.
If you want do some string manipulation, look into the stdlib. Unless you are doing this for class.
Your writing everything to the end of the temp. buffer
You need to add an extra character at the end of the strings for the null byte (I think this implementation may allow for a seg. fault)
I have a program to find and replace words in C++.
#include<iostream.h>
#include<string.h>
int main()
{
char string[80], replace[80], found[80], str1[80], str2[80], str3[80];
cout << "\nEnter string(max 3 words)\n";
cin.getline(string , 80);
cout << "\nEnter the word to be Found\n";
cin.getline(found , 80);
cout << "\nReplace with \n";
cin.getline(replace , 80);
for(int i = 0; string[i] != '\0'; i++)
{
str1[i] = string[i];
if(str1[i] == " ")
break;
}
for(int j = i; string[j] != '\0'; j++)
{
str2[j] = string[j];
if(str2[j] == " ")
break;
}
for(int k = j; string[k] != '\0'; k++)
{
str3[k] = string[k];
if(str3[k] == " ")
break;
}
cout << str1;
cout << str2;
cout << str3;
}
For this I stored every word as a different string, but it doesn't help.
What should be done to improve this?
Your code has too many logical & syntactical error.
Here is the modified code which will accept the required string and print expected output:
#include<iostream>
#include<string.h>
using namespace std;
void strreplace(string orgString, const string search, const string replace )
{
for( size_t pos = 0; ; pos += replace.length() )
{
pos = orgString.find( search, pos );
if( pos == string::npos )
break;
orgString.erase( pos, search.length() );
orgString.insert( pos, replace);
cout<<"String after replacement:"<<orgString<<endl;
}
}
int main()
{
char string[80], replace[80], found[80], str1[80], str2[80], str3[80] ;
cout << "\nEnter string(max 3 words)\n" ;
cin.getline(string , 80);
cout <<"\nEnter the word to be Found\n";
cin.getline(found , 80);
cout <<"\nReplace with \n" ;
cin.getline(replace , 80);
strreplace(string, found, replace);
return 0;
}
I hope this will help you.
In your current code you need to:
Use single quotes to compare characters for equality, not double quotes
Increment another index in your second and third loops. This is because the index for str2 and str3 needs to start at 0, not at the current position being looked at in string
Initalize the main string index (i) in second and third loops with (current value + 1) to skip past the space that it is currently at.
Null terminate your str1, str2, str3
1
if(str1[i] == " ")
should be
if(str1[i] == ' ')
2,3 Instead of
for(int j = i;string[j] != '\0' ; j++)
do
for (int j = 0, i = (i + 1); string[i] != '\0'; j++,i++)
The assignment becomes
str2[j] = string[i];
Do the same for the 3rd loop (without the int in front of j or use another letter). For consistency you could add a j variable starting at 0 to the first loop as well.
4 After each loop add an assignment statement for the null terminator (every c-string needs '\0' at the end to work properly) :
str1[i] = '\0';
str2[j] = '\0';
str3[j] = '\0';
std::string doesn't contain such function instead you could use stand-alone replace function from algorithm header.
#include <algorithm>
#include <string>
string stringReplace(std::string toSearch, std::string toReplace, std::string originalString) {
std::replace( originalString.begin(), originalString.end(), 'toSearch', 'toReplace'); // replace all 'toSearch' to 'toReplace'
return originalString;
}
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 8 years ago.
Improve this question
Trying to implement a fairly simple program in C++. I'm kinda new to this language. But it doesn't seem to be working.
#include <iostream>
#include <string>
using namespace std;
bool isUnique(string);
int main(){
bool uniq;
string a;
cout << "Please input a string, not a very long one...."<< endl;
getline(cin, a);
uniq = isUnique(a);
if (uniq == true)
{
cout << "The string has no repeatations." <<endl;
}else{
cout << "The characters in the string are not unique." <<endl;
}
return EXIT_SUCCESS;
}
bool isUnique(string str){
int len = strlen(str);
bool uniq = true;
for (int i = 0; i <= len; ++i)
{
for (int j = i+1; j <= len; ++j)
{
if (str[j] == str[i])
{
uniq = false;
}
}
}
return uniq;
}
The program compiles but has some logical errors I suppose. Any help appreciated.
An simple criterion for uniqueness is that there are no repeated characters in the sorted range of characters. There are algorithms in the standard library for this:
#include <algorithm> // for std::sort, std::unique
#include <iostream> // for std::cin, std::cout
#include <string> // for std:getline, std::string
int main()
{
std::string input;
std::cout << "Please input a string, not a very long one: ";
std::getline(input, std::cin);
std::sort(input.begin(), input.end());
bool u = std::unique(input.begin(), input.end()) == input.end();
if (u) { std::cout << "Every character is unique.\n"; }
else { std::cout << "The string contains repeated characters.\n"; }
}
As an optimization, you can exit early if the string has more characters than there are unique characters, though you'd need some way to determine what that number is.
You can check uniqueness much easier without a nested loop: make an array of bool[256], cast char to unsigned char, and use as an index into the array. If a bool has been set, the characters are not unique; otherwise, they are unique.
bool seen[256];
for (int i = 0 ; i != str.length() ; i++) {
unsigned char index = (unsigned char)str[i];
if (seen[index]) return false;
seen[index] = true;
}
return true;
The idea is simple: you mark characters that you've seen as you go, returning false if you see a "marked" character. If you reach the end without returning, all characters are unique.
This algorithm is O(n); your algorithm is O(n2). This does not make much difference, though, because it is impossible to construct a string of unique characters that is longer than 256 characters.
You are using a string, so it is not necessary to convert it to a char array. Use the string to check. You can check it like this:
bool isUnique(string str){
for (std::string::size_type i = 0; i < str.size(); ++i)
{
if(i < str.size()-1){
for (std::string::size_type j = i+1; j < str.size(); ++j)
{
if (str[j] == str[i])
{
uniq = false;
}
}
}
}
return uniq;
}
you can try this:
int main () {
bool uniqe=false;
string a;
char arr[1024];
int count[256]={0};
cout << "Please input a string, not a very long one...."<< endl;
getline(cin, a);
strcpy(arr, a.c_str());
for(int i=0;i<strlen(arr);i++)
count[(int)(arr[i])]++; // counting the occurence of character
for(int i=0;i<256;i++){
if(count[i]>1){ // if count > 1 means character are repeated.
uniqe=false;
break;
}else{
uniqe=true;
}
}
if(uniqe)
cout << "The string has no repeatations." <<endl;
else
cout << "The characters in the string are not unique." <<endl;
return 0;
}
There are too many errors in your code. For example instead of
int len = sizeof(arr)/sizeof(*arr);
there shall be
size_t len = std::strlen( arr );
Or instead of
for (int i = 0; i <= len; ++i)
there shall be at least
for (int i = 0; i < len; ++i)
and so on.
And there is no any need to define a character array. Class std::string has all that is required to do the task.
Try the following function
bool isUnique( const std::string &s )
{
bool unique = true;
for ( std::string::size_type i = 0; i < s.size() && unique; i++ )
{
std::string::size_type j = 0;
while ( j < i && s[j] != s[i] ) ++j;
unique = j == i;
}
return unique;
}
Here is a demonstrative program
#include <iostream>
#include <iomanip>
#include <string>
bool isUnique( const std::string &s )
{
bool unique = true;
for ( std::string::size_type i = 0; i < s.size() && unique; i++ )
{
std::string::size_type j = 0;
while ( j < i && s[j] != s[i] ) ++j;
unique = j == i;
}
return unique;
}
int main()
{
std::string s( "abcdef" );
std::cout << std::boolalpha << isUnique( s ) << std::endl;
s = "abcdefa";
std::cout << std::boolalpha << isUnique( s ) << std::endl;
return 0;
}
The output is
true
false
Here is your code with the errors fixed:
#include <iostream>
using namespace std;
bool isUnique(string,int); //extra parameter
int main(){
bool uniq;
string a;
cout << "Please input a string, not a very long one...."<< endl;
getline(cin, a);
uniq = isUnique(a,a.length()); //pass length of a
if (uniq == true)
{
cout << "The string has no repeatations." <<endl;
}else{
cout << "The characters in the string are not unique." <<endl;
}
return EXIT_SUCCESS;
}
bool isUnique(string str,int len){
bool uniq = true;
for (int i = 0; i < len-1; ++i) //len-1 else j would access unitialized memory location in the last iteration
{
for (int j = i+1; j < len; ++j) //j<len because array index starts from 0
{
if (str[j] == str[i])
{
uniq = false;
}
}
}
return uniq;
}
This was the interview question:
How to convert Dogs like cats to cats like Dogs ?
My code shows: cats like cats. Where am I making the mistakes?
#include <iostream>
using namespace std;
int main()
{
char sentence[] = ("dogs like cats");
cout << sentence << endl;
int len = 0;
for (int i = 0; sentence[i] != '\0'; i++)
{
len++;
}
cout << len << endl;
char reverse[len];
int k = 0;
for (int j = len - 1; j >= 0; j--)
{
reverse[k] = sentence[j];
k++;
}
cout << reverse << endl;
int words = 0;
char str[len];
for (int l = 0; reverse[l] != '\0'; l++)
{
if (reverse[l] == ' ' || reverse[l] == '\0') // not sure about this part
{
for (int m = l; m >= 0; m--)
{
str[words] = reverse[m];
words++;
}
}
}
cout << str;
return 0;
}
I know you can do this using pointers, stack, vectors... but interviewer was not interested in that!
This is a fixed version of your sample code:
Your principal problem is that every time you found and ' ' or '\0' you copy the bytes of the reverse string from the beginning to that point. Example in loop 5 you copy from index 0-5 (stac) from reverse to str in reverse order, but in in loop 10 you copy from index 0-10 (stac ekil) from reverse to str in reverse order, until here you have already the printed result string ('cats like cats'), and the same in loop 15 all of this incrementing the index of str, in the last loop you are written pass the end of the valid memory of str (and because of that not printed as output).
You need to keep track when end the last word reversed to reverse only the actual word, and not the string from the beginning to the actual index.
You don't want to count the special character (' ' and '\0') in the reversing of the words, you would end with cats like\0dogs
Modified sample code provided:
#include <iostream>
using namespace std;
int main() {
char sentence[] = ("dogs like cats");
cout << sentence << endl;
int len = 0;
for (int i = 0; sentence[i] != '\0'; i++) {
len++;
}
cout << len << endl;
char reverse[len];
int k = 0;
for (int j = len - 1; j >= 0; j--) {
reverse[k] = sentence[j];
k++;
}
cout << reverse << endl;
int words = 0;
char str[len];
// change here added last_l to track the end of the last word reversed, moved
// the check of the end condition to the end of loop body for handling the \0
// case
for (int l = 0, last_l = 0; ; l++) {
if (reverse[l] == ' ' || reverse[l] == '\0')
{
for (int m = l - 1; m >= last_l; m--) { // change here, using last_t to
str[words] = reverse[m]; // only reverse the last word
words++; // without the split character
}
last_l = l + 1; // update the end of the last
// word reversed
str[words] = reverse[l]; // copy the split character
words++;
}
if (reverse[l] == '\0') // break the loop
break;
}
cout << str << endl;
return 0;
}
Some code, written with the restriction of using the most simple features of the language.
#include <iostream>
// reverse any block of text.
void reverse(char* left, char* right) {
while (left < right) {
char tmp = *left;
*left = *right;
*right = tmp;
left++;
right--;
}
}
int main() {
char sentence[] = "dogs like cats";
std::cout << sentence << std::endl;
// The same length calculation as sample code.
int len = 0;
for (int i = 0; sentence[i] != '\0'; i++) {
len++;
}
std::cout << len << std::endl;
// reverse all the text (ex: 'stac ekil sgod')
reverse(sentence, sentence + len - 1);
// reverse word by word.
char* end = sentence;
char* begin = sentence;
while (end < sentence + len) {
if (*end != ' ')
end++;
if (end == sentence + len || *end == ' ') {
reverse(begin, end - 1);
begin = end + 1;
end = begin;
}
}
std::cout << sentence << std::endl;
return 0;
}
Dissecting your algorithm in pieces. First, you find the length of the string, not including the null char terminator. This is correct, though could be simplified.
size_t len = 0;
for (int i = 0; sentence[i] != '\0'; i++) {
len++;
}
cout << len << endl;
This could easily be written simply as:
size_t len = 0;
while (sentence[len])
++len;
Next, you reverse the entire string, but the first defect surfaces. The VLA (variable length array) you declare here, (which you don't need and shouldn't use, as it is a C++ extension and non-standard) does not account for, nor set, a terminating null-char.
char reverse[len]; // !! should be len+1
int k = 0;
for (int j = len - 1; j >= 0; j--) {
reverse[k] = sentence[j];
k++;
}
// !! Should have reverse[k] = 0; here.
cout << reverse << endl; // !! Undefined-behavior. no terminator.
This temporary buffer string is not needed at all. There is no reason you can't do this entire operation in-place. Once we calculate len correctly, you simply do something like the following to reverse the entire sequence, which retains the null char terminator in proper position:
// reverse entire sequence
int i = 0, j = len;
while (i < j--)
{
char c = sentence[i];
sentence[i++] = sentence[j];
sentence[j] = c;
}
Next we move to where you try to reverse each internal word. Again, just as before, the buffer length is not correct. It should be len+1. Worse (hard to imagine), you never remember where you left off when finding the end point of a word. That location should be the next point you start checking for, and skipping, whitespace. Without retaining that you copy from current point all the way back to the beginning of the string. which essentially blasts cats over dogs.
int words = 0;
char str[len]; // !! should be len+1
for (int l = 0; reverse[l] != '\0'; l++)
{
if (reverse[l] == ' ' || reverse[l] == '\0') // not sure about this part
{
for (int m = l; m >= 0; m--) {
str[words] = reverse[m];
words++;
}
}
}
cout << str; //!! Undefined behavior. non-terminated string.
Once again, this can be done in-place without difficulty at all. One such algorithm looks like this (and notice the loop that reverses the actual word is not-coincidentally the same algorithm as reversing our entire buffer):
// walk again, reversing each word.
i = 0;
while (sentence[i])
{
// skip ws; root 'i' at beginning of word
while (sentence[i] == ' ') // or use std::isspace(sentence[i])
++i;
// skip until ws or eos; root 'j' at one-past end of word
j = i;
while (sentence[j] && sentence[j] != ' ') // or use !std::isspace(sentence[j])
++j;
// remember the last position
size_t last = j;
// same reversal algorithm we had before
while (i < j--)
{
char c = sentence[i];
sentence[i++] = sentence[j];
sentence[j] = c;
}
// start at the termination point where we last stopped
i = last;
}
Putting It All Together
Though considerably simpler to use pointers than all these index variables, the following will do what you're attempting, in place.
#include <iostream>
int main()
{
char s[] = "dogs like cats";
std::cout << s << '\n';
size_t len = 0, i, j;
while (s[len])
++len;
// reverse entire sequence
i = 0, j = len;
while (i < j--)
{
char c = s[i]; // or use std::swap
s[i++] = s[j];
s[j] = c;
}
// walk again, reversing each word.
i = 0;
while (s[i])
{
// skip ws; root 'i' at beginning of word
while (s[i] == ' ') // or use std::isspace
++i;
// skip until ws or eos; root 'j' at one-past end of word
j = i;
while (s[j] && s[j] != ' ') // or use !std::isspace
++j;
// remember the last position
size_t last = j;
while (i < j--)
{
char c = s[i]; // or use std::swap
s[i++] = s[j];
s[j] = c;
}
// start at last-left posiion
i = last;
}
std::cout << s << '\n';
return 0;
}
Output
dogs like cats
cats like dogs
My advise would be to break up the original string into an array of words, reverse that array. Then add those words to your reversed sentence with a space in between.
Since they asked for no libraries, I assumed no std::string, no vectors, nothing at all and so I wrote it in C.. the only thing used is printf. Everything else is from scratch :l
The idea is that you reverse the array first. Then split the array by space and reverse each word.
Example: http://ideone.com/io6Bh9
Code:
#include <stdio.h>
int strlen(const char* s)
{
int l = 0;
while (*s++) ++l;
return l;
}
void reverse(char* str)
{
int i = 0, j = strlen(str) - 1;
for(; i < j; ++i, --j)
{
str[i] ^= str[j];
str[j] ^= str[i];
str[i] ^= str[j];
}
}
void nulltok(char* str, char tok, int* parts)
{
int i = 0, len = strlen(str);
*parts = 1;
for (; i < len; ++i)
{
if (str[i] == tok)
{
str[i] = '\0';
++(*parts);
}
}
}
char* reverse_sentence(char* str)
{
char* tmp = str;
reverse(str);
int i = 0, parts = 0, len = strlen(str);
nulltok(str, 0x20, &parts);
while(parts--)
{
reverse(str);
str += strlen(str) + 1;
}
for(; i < len; ++i)
if (tmp[i] == '\0')
tmp[i] = 0x20;
return tmp;
}
int main(void)
{
char str[] = "dogs like cats";
printf("%s", reverse_sentence(str));
return 0;
}
My solution
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
string str;
cout<<"enter the sentence"<<endl;
getline(cin,str);
char* pch;
pch = strtok((char*)str.c_str()," ");
string rev = "";
while(NULL != pch)
{
rev.insert(0,pch);
rev.insert(0," ");
pch = strtok(NULL," ");
}
cout<<"the reversed string is :"<<rev<<endl;
return 0;
}