unable to convert integer to string.

i was trying to solve a problem in codechef .when i started writing its code i realised that i needed to covert a integer to string.
i did this

char *instr=itoa(num);
string s=string(instr);

but it is showing error  itoa() was not declared in this scope  .where i am going wrong.my full code goes like this:-
#include #include #include using namespace std; int palin(long int num) { char *instr=itoa(num); string s=string(instr); int flag=0; for(int i=0,j=s.length();i>i; while(x==0 || y==0) { y=prime(i); if(y==1) x=palin(i); if(x==0 || y==0) { i++; x=0; y=0; } } cout<<i<<endl; return 0; } ``` any help shall be highly appreciated

See if including “#include<bits/stdc++.h” solves the problem or not.

Else refer here - https://stackoverflow.com/questions/5590381/easiest-way-to-convert-int-to-string-in-c

EDIT: itoa isnt available in c++, instead, use to_string() function.

PS: Your prime function has 2 errors, and also check X. Your code has atleast 4-5 bugs which are going to chomp you down in debugging. XD

Here is the code which compiles and runs in C++14, (G 4.9.2)

#include <iostream>
#include <string>
#include <stdlib.h>

using namespace std;
int palin(long int num)
{
    //char *instr=itoa(num);
    string s=to_string(num);
    int flag=0;
    for(int i=0,j=s.length()-1;i<s.length()/2;i++,j--)
    {
        if(s[i]!=s[j])
        {
        flag=1;
        break;
        }
    }
    if (flag==1)
        return 0;
    else return 1;


}


int prime(int j)
{
    for(int i=2;i<=j/2;i++){
        if(j%i==0)
            return 0;
    }
    return 1;
}


int main()
{
 long int i;
 int x=0,y=0;
 cin>>i;
 while(x==0 || y==0)
 {
 y=prime(i);
 if(y==1)
 x=palin(i);


if(x==0 || y==0)
 {
    i++;
    x=0;
    y=0;


}


}
cout<<i<<endl;
return 0;
}

I also fixed errors in your palin function (It is here - for(int i=0,j=s.length()-1;i<s.length()/2;i++,j--) Here, j should be as “j=s.length()-1” because j=s.length will throw out of index thing, which causes undefined behavior. Here this caused your function to always return 0 and end up as a TLE )

1 Like

@vijju123 no it doesn’t help.showing same error again.
i already refeered to the link before asking this question .even to_string(num) is not working.

Change it to string s= to_string (num) ; It works, i compiled your code.

@vijju123 i replaced it as u said but to_string(num) giving me same error message how did ur code compile.

@vijju123 thanks for pointing out errors in prime function.corrected them.

Wait, i am uploading a screen shot and the compiled code.

There were errors in string part due to error in prime function and other places. I fixed them as well (thats how i was able to comment that the code has errors )

the reason to_string() was giving me error was that i was compiling my code in c++ 4.9.2(GCC 4.9.2).GOT THE PROGRAM EXECUTED NOW…

prefer C++ 14 because it has features which C++ 4.9.2 doesnt have :slight_smile:

@vijju123 when i am taking long value of number(say 462895) i am geeting TLE .how to overcome that.

corrected TLE Bug .thanks for all ur help.

Yes, a TLE is expected for very large number. You can use sieve of erastothenes to find priems upto 10^7 and store them in array/vector and use it.
Trick is that, during sieve you can store the prime numbers in an array like-

int arr[10000];
k=0;
.
.
.
sieve()
if(isPrime(num))
 arr[k++]=num

Give me some time, I am caught up atm. I will give you a AC code if you want ^^

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