String to int conversion - the result is always 0

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1.00/5 (1 vote)

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C++

#include "stdafx.h"
#include <stdlib.h>
#include <iostream>
#include <string>
using namespace std;
//#include <stdlib.h>   // for itoa() call
//#include <stdio.h>    // for printf() call
int main() 
{
    string strConvert;
    cout<<"sentence"<<endl;
    cin>>strConvert;
    int intReturn;
    intReturn = atoi(strConvert.c_str());
    cout<<intReturn<<endl;
}

Posted 13-Feb-11 20:22pm

mf_arian

Updated 13-Feb-11 21:29pm

Nuri Ismail

v3

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ShilpiP · Accepted Answer · 2011-02-13T20:34:00

Solution 1

When I execute your program it gives me right result.
As MSDN says :

If the input cannot be converted to a value of that type, the return value is 0

Posted 13-Feb-11 20:34pm

ShilpiP

Nuri Ismail · Accepted Answer · 2011-02-13T21:12:00

As Shilpi Boosar already said, the input string must be a valid integer, otherwise the result will be 0.

If all you want is to accept only integers as input you can use this:

C++

int intReturn;
if(std::cin >> intReturn)
{
    // We will get here only if the input is valid integer
    std::cout << intReturn;
}

For a conversion from string to int you can also use (as an alternative to atoi):

C++

std::string str = "567";
std::istringstream iss(str);
int intReturn;
if(iss >> intReturn)
{
    // We will get here only if the conversion is successful
    std::cout << intReturn;
}

Using stringstreams for string to type and type to string conversions is described here[^]. See items: 39.1, 39.2 and 39.3. :)

If you read this items you will find out that stringstream conversion is not just an alternative to atoi. Using stringstreams you can convert an arbitrary type T to string if provided T supports syntax like std::cout << x. :)