I wrote a code to check if a string is a Palindrome or not. I assume logically my code is correct but the usage of strrev() function is incorrect. Please can anyone view it once? Thanks in advance
#include<iostream>
#include<string.h>
using namespace std;
int main(){
char name[100];
int result;
cout<<name<<endl;
result=strcmp(name,strrev(name));
if(result==0){
cout<<"YES";
}
else{
cout<<"NO";
}
return 0;
}
strrev is not a standard C function, so it is anyone's guess as to what it actually does. In case if it operates on the passed string in-place then the construction strcmp(name,strrev(name)) is wrong as it will always return 0 (the strings are equal). And, of course, the fact that you don't initialize name is also an error.
First off, name is not even initialized. It does not hold any string whatsoever, it holds garbage value. So you should first either take user input using cin >> name; or just explicitly initialize it at point of declaration using char name[100] = "yourString"
Secondly, strrev will reverse the given string before returning it. So when you do strcmp(name, strrev(name)). strrev(name) already reverses the actual name string before strcmp can execute. So you're always comparing the same strings. You should compare a copy of name instead.
Like so-
char name[100], temp[100];
std::cin >> name;
strcpy(temp, name);
Now you should be able to print the result like before-
if (result == 0)
{
std::cout << "YES\n";
}
else
{
std::cout << "NO\n";
}
Also, off topic but you don't have to explicitly store the result, you can directly compare the strcmp result like so -
if (!strcmp(name, _strrev(temp)))
{
std::cout << "YES\n";
}
else
{
std::cout << "NO\n";
}
Or you could use ternary operator -
std::cout << strcmp(name, _strrev(temp)) ? "NO\n" : "YES\n";
Here's the full program-
#include<iostream>
#include<string>
int main()
{
int result;
char name[100], temp[100];
std::cin >> name;
strcpy(temp, name);
std::cout << strcmp(name, _strrev(temp)) ? "NO\n" : "YES\n";
return 0;
}
Last but not the least, please consider not using strrev, it is a very old C standard function. You should use std::reverse instead and operate using std::string instead of C-Style strings. If you still want to keep using C style strings, use _strrev if that is available to you.
More info on C and C++ style strings
Related
This question already has answers here:
Compare equality of char[] in C
(5 answers)
Closed 6 years ago.
The for loop reverses original string 's' and stores it in 'temp.'Temp is printed correctly. After which, s and temp are compared, but the result always shows NO. :(
#include<cstring>
#include <iostream>
using namespace std;
int main()
{
char s[100], temp[100];
cin >> s;
cout << strlen(s);
for(int i=0;i<strlen(s);i++)
{
temp[i]=s[strlen(s)-i];
}
cout << "temp is" << temp;
if(temp==s)
{
cout << "YES";
}
else
{
cout << "NO";
}
return 0;
}
You should use strcmp instead of == because the latter is merely a pointer comparison. Also, '\0' has to be used to end your string. And your current code would actually create an empty string because your string at position strlen(s) contains '\0'.
Then again, you should not work with char arrays in C++ on your own, rather use std::string as already pointed out in comments.
I've recently started learning programming using the C++ language. I wrote a simple program that is supposed to reverse a string which I compile in the Terminal using gcc/g++.
#include <iostream>
using namespace std;
string reverse_string(string str)
{
string newstring = "";
int index = -1;
while (str.length() != newstring.length())
{
newstring.append(1, str[index]);
index -= 1;
}
return newstring;
}
int main()
{
string x;
cout << "Type something: "; cin >> x;
string s = reverse_string(x);
cout << s << endl;
return 0;
}
I've rewritten it multiple times but I always get the same output:
Type something: banana
��
Has anyone had a problem like this or know how to fix it?
Your code initializes index to -1, and then uses str[index] but a negative index has no rational meaning in C++. Try instead initializing it like so:
index = str.length() - 1;
I can see several issues with your code. Firstly, you are initializing index to -1, and then decrementing it. Maybe you meant auto index = str.length()-1;?
I recommend you look at std::reverse, which will do the job you're after.
Your main function then becomes:
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
int main()
{
string x;
cout << "Type something: ";
cin >> x;
reverse(x.begin(), x.end());
cout << x << endl;
return 0;
}
If you really want to write your own reverse function, I recommend iterators over array indices. See std::reverse_iterator for another approach.
Note, the above will simply reverse the order of bytes within the string. Whilst this is fine for ASCII, it will not work for multi-byte encodings, such as UTF-8.
You should use a memory debugger like valgrind.
It's a good practice to scan your binary with it, and will make you save so much time.
this script is supposed to output array values that were inputted by the user into array "store." I am trying to store all the char array values into string temp. I get the error on line 12: "[Error] invalid conversion from 'char*' to 'char' [-fpermissive]." Would appreciate any help!
Edit: so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so? The cmd only correctly couts the first string but after the space, it messes up.
#include <iostream>
#include <cstdlib>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50];
cout << "enter text: " << endl;
cin >> store;
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Using input from all answerers I finally got the fixed code:
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50] = {0};
cout << "enter text: " << endl;
cin.getline(store, 50);
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max && store[i]!=0)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Thanks everyone. i learned a lot!!!
When you get an input using "cin" your input automatically ends with 0 (NULL).
You just need to add one little piece of code to your while statement.
instead of this :
while (i < max)
use this :
while (i < max && store[i]!=0)
Now it will stop when the input string is finished and won't print any garbage existed in the array beforehand.
To show that cin does add terminating zero, i initialized the array to 46, and put a breakpoint after the cin
so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so?
Not sure what you mean by jumbled up. But since you did not tell us what you typed its hard to know it looks like it worked to me:
> ./a.out
enter text:
Plop
Plop�ȏU�
Notice that since my input is only 4 characters long. This means that a lot of the characters in the array still have undefined (ie random values). This is why I am seeing junk. To get past this initialize the array to have all 0 values.
char store[50] = {0};
Even bettern use a C++ object than handles longer strings.
std::string store;
std::getline(std::cin, store);
Note: passing arrays to functions by value is not a good idea. On the other end they have decayed to pointers and thus do not act like arrays anymore (they act like pointers whose semantics are similar but not identical).
If you must pass an array pass it by reference. But I would use a C++ container and pass that by reference (it is much safer than using C constructs). Have a look at std::string
The declaration of the function is wrong. Should be void coutArray(char *, int);
Look at the Implicit Conversion rules to understand what the compiler can do and what it cannot to do for you.
The issue with your program was that you were probably entering in less characters than the maximum size of the buffer. Then when you passed the maximum size as the parameter to coutArray, you assigned unfilled slots in the char array to temp. These unfilled slots could contain anything, as you have not filled them up to that point.
Your program is still correct, but what would be better would be to use read so that the number of bytes you specify is the minimum number of bytes that can be entered:
std::cin.read(store, 50);
Even better solution would be to use std::string:
std::string store;
std::cin >> store;
// or for the entire line
std::getline(std::cin, store);
It also follows that your coutArray should be changed to:
void coutArray(std::string);
// ...
void coutArray(std::string str)
{
std::cout << str << std::endl;
}
Look at this way
template<typename T, size_t N>
void MyMethod(T (&myArray)[N])
{
//N is number of elements, myArray is the array
std::cout<<"array elements number = "<<N<<endl;
//put your code
string temp;
temp.resize(N+1);//this is for performance not to copy it each time you use += operator
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
//call it like this
char arr[] = "hello world";
MyMethod(arr);
Please tell me why my code to reverse the input string is giving me various errors.
#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
void ReverseString(string &aString);
int main(){
string info;
cout << "What's your string?" << endl;
getline(cin, info);
ReverseString(info);
cout << ReverseString(string info) << " compare with: " << info << endl;
system("pause");
return 0;
}
void ReverseString(string &aString){
for(int i = 0; i < aString.length(); i++)
{
string temp = 0; // initialize temporary string
temp = temp + aString.at(aString.length() - 1 - i); // hold temporary string
if(i => aString.length()) /*assign temp string to aString when all chars are processed*/
{
temp = &aString;
}
}
}
Hi you could simplify your code a lot by using the STL
for example:
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
std::string str = "Hello World";
cout << str << endl;
std::reverse(str.begin() , str.end());
cout << str << endl;
return 0;
}
let me know if this is not suitable to your needs as theres a few other ways to do it too.
Without STL:
There are some corrections/changes to your code required, which I have supplied below. However you may want to look at some documentation on referencing variables to get an idea of how it works, such as:
http://www.cprogramming.com/tutorial/references.html
http://www.thegeekstuff.com/2013/05/cpp-reference-variable/
http://en.wikipedia.org/wiki/Reference_(C++)
What is a reference variable in C++?
http://www.tutorialspoint.com/cplusplus/cpp_references.htm
Correct reference and pointer use is a major part of C++ and allows for some of the most powerful functionality in the language, provided it is used correctly, or major headaches and mental scarring if used incorrectly, so it is worth, even essential, to have a firm grasp of them.
And even then expect the odd misuse to crop up every-so-often. :)
#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
void ReverseString(string &aString);
int main(){
string info;
cout << "What's your string?" << endl;
getline(cin, info);
cout << info << " compare with: ";
ReverseString(info);
cout << info << endl;
system("pause");
return 0;
}
void ReverseString(string &aString)
{
int len = aString.length();
string temp = aString;// initialize temporary string
aString ="";
for(int i = 0; i < len; i++)
{
aString += temp[len - (1+ i)]; // assigns the reversed value to the referenced string
}
}
Just noticed the quote below from #zac-howland : so true, I have however left the code in as an illustrative piece. Provided some reading is done on this as well as plenty of experimentation I hope NewProgrammer will get the information and skill-set he needs to go forward.
#include<iostream>
#include<string>
#include <algorithm>
using namespace std;
string info;
string rvrs(string &str)
{
std::reverse(str.begin(),str.end());
return str;
}
int main()
{
cout<<"What is your string :: ";
getline(cin,info);
cout<<rvrs(info);
cout<<endl;
return 0;
}
You have a few syntactical errors in addition to your logical ones:
cout << ReverseString(string info) << " compare with: " << info << endl;
ReverseString(string info) will pass in an empty string to your ReverseString function (if it even compiles - which looks like it should not since you have 2 info's in the same scope). What you wanted is:
cout << ReverseString(info) << " compare with: " << info << endl;
In your reverse function, you only need to go to length() / 2.
Since you are passing by reference, changes you make to the string within the function will be reflected in the object you passed into it. That is, the original info will be reversed. If you want it to operate on a copy, you need to pass it by copy, not by reference.
Finally, cout << ReverseString(info) is not useful (if it even compiles) as ReverseString returns a void. You should have it return a string (the reversed string).
You have a number of problems.
string temp = 0; // initialize temporary string
It doesn't really make sense to initialize a string to 0. Just string temp; would be fine here.
temp = temp + aString.at(aString.length() - 1 - i); // hold temporary string
That's not quite how I'd do things, but I guess it should work.
if(i => aString.length())
This condition doesn't seem to make sense. Your loop is defined to iterate with i going from 0 to the length of the string -1, so it can never be greater than or equal to the string length.
/*assign temp string to aString when all chars are processed*/
{
temp = &aString;
}
Here the code doesn't match the comment. The comment says you're going to assign to aString, but the code assigns something to temp. The comment is probably closer to what you really want. But you still need to fix the condition, and probably want to do this after the loop has finished executing. So in pseudo-code, you'd end up with something like:
for (all characters in the string)
add the next character in the string to the end of temp
assign temp back to the original string
I am new to programming and attempted to improve on my basic countdown timer. I don't know why I'm getting this error and other questions are in different situations and therefore don't suit my program.
//countdown timer using while loops, if else, strings and sleep
#include <iostream>
#include <windows.h>
#include <string>
using namespace std;
int main ()
{
char progend[5];
float a; /* a will be floating point */
cout << "Enter start the the number you want to count down from" << ".\n";
while (a>-1) { /* the main program is located here */
cin >> progend[5];
if (progend[5] = "end") /* if the user inputs end the program ends */
{
a = -1;
}
else if (progend [5] = "start")
{
cin >> a;
while (a>0) { /* the actual countdown timer*/
Sleep(100);
a = a - 0.1;
cout << a;
}
cout << "Finished!" << ".\n" << "Enter start then enter another number to count down from or enter end to close the program" << ".\n";
}
else
{
cout << "Enter yes or end";
}
}
return 0;
}
Any help would be appreciated.
char progend[5];
...
if (progend [5] = "start")
tries to assign string literal "start" to 6th character of progend array (which doesn't even exist). Note that even if this code tried to assign a character, writing into the array after its end would cause undefined behavior.
You could either use C-style strcmp:
if (strcmp(progend, "start") == 0)
or yet even better: since this is C++, use std::string objects instead:
std::string progend;
...
if (progend == "start") ... // <-- this will use std::string::operator==
You're trying to assign a char* to char, I'm assuming you want to compare .
So use strstr
if (strstr(progend,"end" )){
//...
}
Similarly all other places
But why not use std::string , when using C++
std::string progend;
if(progend.find("end") != std::string::npos)
{
}
You are assigning a const char * to a char variable in
if (progend[5] = "end")
progend[5] is an element of a char array that holds a char value. "end" cannot be assigned to it.
You can use std::string. Then compare it like
std::string progend;
...
if(progend == "end")
{
//your code
You made a number of different errors.
cin >> progend[5];
Here, you ask for a character input, instead of a string. What is more, index 5 is out of the bounds of the array (we start counting from 0).
progend[5] = "start"
Here, there are two errors. To compare for equality, you sholud use == instead of =. What you actually did is try to assign a value. What is more, "start" is a C-type String, or better a pointer to the first character of the String.
Why don't you simply use a String from the C++ STL?
#include <string>
using namespace std;
// etc.
String progend;
Also, replace all instances of progend[5] with progend, you are not refering to a specific position. Equality check must also be ==.
I hope this helps!!! :D