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Strings to Numbers

Using stringstream class

#include <iostream>
#include <sstream>
using namespace std;

int main()
    string s = "12345";

    stringstream geek(s);

    int x = 0;
    geek >> x;

    cout << "Value of x : " << x;

    return 0;


sscanf() is a C style function similar to scanf(). It reads input from a string rather that standard input.

const char *str = "12345";
int x;
sscanf(str, "%d", &x);
printf("\nThe value of x : %d", x);


int stoi (const string&  str, size_t* index = 0, int base = 10): string to value
int atoi (const char * str) : character array or string literal tp value.
stoi() vs atoi()
atoi stoi
legacy c style function c++11
c char and string literal c++ string
1 parameter 3 parameters: string, start index, base

String to Double

atof(): the converted integral number as an int value. If no valid conversion could be performed, it returns zero.