C++

Examples, hints, and tips to help you code better in C++.

Convert a string to an integer using scanf and sscanf

int scanf ( const char * format, ... );
int sscanf ( const char * str, const char * format, ...);

Getting input from keyboard (stdin)

// NOTE: this uses scanf
#include <stdio.h>
int main()
{
     int i;
     printf( "Enter an integer: " );
     if( scanf( "%d", &i ) <=0 )
     {
          printf ("ERROR");
     }
     else
     {
          printf ("The integer value is: %d.",i);
     }
     return 0;
}

Convert stdin string input to an integer using cin

#include <iostream>
#include <limits>
 
using namespace std;
 
int main ()
{
    int i;
    cout << "Enter an integer: ";
    cout.flush();
    while ( (cin >> i).fail() )
    {
        // Clear the error flag in the cin object
        cin.clear();
        // Discard the erroneous user input
        cin.ignore(numeric_limits<streamsize>::max(), 'n');
        cout << "Please try again: ";
        cout.flush();
    }
    cout << "The integer value is: " << i;
}

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Convert a string to an integer using a stringstream

Using a const char*

#include <sstream>
#include <iostream>  //used for cout
int main()
{
    const char* str = "12345";
    std::stringstream ss( str );
    int i;
    ss >> i;
    if (ss.fail())
    {
        // Error
    }
    else
    {
        std::cout << "The integer value is: " << i;
    }
    return 0;
}

Convert a string to an integer using the boost lexical_cast

#include <boost/lexical_cast.hpp>
#include <string>
int main()
{
    std::string str = "12345";
    int i;
    try
    {   
        i = boost::lexical_cast<int>(str);
    }
    catch( const boost::bad_lexical_cast & )
    {
        //unable to convert
    }
 
    return 0;
}

Convert a string to an integer using atoi

int atoi ( const char * str );

Getting input from keyboard (stdin)

#include <stdio.h>
#include <stdlib.h>
int main ()
{
    int i;
    char str[256];
    printf ("Enter a number: ");
    fgets ( str, 256, stdin );
    i = atoi (str);
    printf ("The integer value is: %d.",i);
    return 0;
}

Using a const char*

#include <stdio.h>
#include <stdlib.h>
int main ()
{
     const char* str = "12345";
     int i = atoi(str);
     printf ("The integer value is: %d.",i);
     return 0;
}

For loop
- C++
- Java
This is an example of a typical for loop.
```
for( int var=0; var<10; var++) {
    // Code to execute    
}
```
The initiation of the for loop includes three different command seperated be semicolons.

First
In this example an integer named var is created and initialized to ;
If we are using a variable that has already being instantiated just enter the name of the variable and optionally assign it a new value.
ie.
```
int var = 0;
for(var=2; var<10; var++) {
    // Code to execute    
}
```
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C++

Convert a string to an integer using scanf and sscanf

Convert stdin string input to an integer using cin

Convert a string to an integer using a stringstream

Convert a string to an integer using the boost lexical_cast

Convert a string to an integer using atoi

For loop

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