convert string to array of integer in c++

Question

Someone will help me, in understanding the while loop in following code about what it does? for example, take input from the user: 1 2 3 8 (input size not given) and one value (any index) show size of an array. it is printing the maximum value of the array. here the answer is 8.

#include<bits/stdc++.h>
#define ll long long 
using namespace std;
int main()
{
    int t;
    cin >> t;
    while(t--)
    {
        string x;
        getline(cin, x);
        ll p;
        istringstream iss(x);// use of this function
        vector<ll> v;
        ll ans;
        while(iss>>p)// what this loop do
        { 
           v.push_back(p);
        }
        ll size=v.size()-1;
        sort(v.begin(), v.end());
        if(size==v[size])
        {  
            ans=v[size-1];
        } 
        else
        {
            ans=v[size];
        }
        cout<<ans<<"\n";
    }
    return 0;
}

My friend has a better explanation for that have a look https://stackoverflow.com/questions/7663709/convert-string-to-int-c — joeydash, Nov 13 '17 at 08:04
You should ignore one character from cin, so you can enter string properly. use cin.ignore(); after cin >> t; :) — Jay Joshi, Nov 13 '17 at 09:20
Possible duplicate of [Convert string to int C++](https://stackoverflow.com/questions/7663709/convert-string-to-int-c) — , Apr 30 '18 at 03:33

score 3 · Accepted Answer · answered Nov 13 '17 at 09:33

3

istringstream iss(x) creates a string stream called iss consisting of the string x. iss >> p extracts the next element from the iss stream and puts it into p. the return value is int because the variable p is of type int.

while(iss>>p)           // get an int value from string stream iss
{ 
     v.push_back(p);    // push the int value to the vector
}

you have to use cin.ignore() after cin. otherwise the next getline function will take only new line character. like this:

cin >> t;
cin.ignore();

answered Nov 13 '17 at 09:33

Jay Joshi

868
8
24

string stream takes only int value not spaces? – Posi2 Nov 13 '17 at 10:39
yes it takes whitespaces, but still you have to ignore one new line character after you use cin. check : https://stackoverflow.com/questions/12691316/getline-does-not-work-if-used-after-some-inputs – Jay Joshi Nov 13 '17 at 10:44
if you give string "1 2 3 4", the istringstream will return 1 , 2 , 3 and 4 in each while loop iteration – Jay Joshi Nov 13 '17 at 10:44
glad to hear that :D. dont forget to check as answer and upvote.! :) – Jay Joshi Nov 13 '17 at 10:45
oh .. hmm.. you can still select as answer and your reputation will increase :) – Jay Joshi Nov 13 '17 at 10:49

omkar · Answer 2 · 2020-11-04T10:28:59.347

1

    string str;
    cin>>str;
    int size = str.size(),arr[size];  //array of size equal to string size
    for(int i=0;i<size;i++)
    {
        arr[i] = (int)str[i]-'0';    //typecasting to int
    }

for str[i]-'0' the explanation is : What is the purpose of using str[i]-'0' where str is a string? Error may occur if unable to typecast

edited Nov 04 '20 at 10:28

answered Mar 22 '20 at 18:02

omkar

71
1
6

Posi2 · Answer 3 · 2018-05-01T06:21:20.773

0

Using function stoi() (for int values) or stol()(for long values) also optionfor integer values.

int n=56; // use #include<bits/stdc++.h>
string s=to_string(n); // we get string "56" that's for integer to string
int x=stoi(substr(index,length));// for string to integer

edited May 01 '18 at 06:21

answered Apr 30 '18 at 02:03

Posi2

144
1
14

This doesn't help at all with handling multiple values – Ben Voigt Apr 30 '18 at 06:25
That's true.Do you know the function to handle multiple values? – Posi2 May 01 '18 at 06:28
`strtol` is pretty good for a list of values, because after parsing each value, it gives back a pointer to what's next – Ben Voigt May 01 '18 at 06:37
It works similar to the `iss>>p` with `cin.ignore()` (as explained above). `strtol` is good for conversion of value. – Posi2 May 01 '18 at 07:15

convert string to array of integer in c++

3 Answers3