This part will cover various techniques for transforming the provided string information into an integer in C++ programming. There are specific scenarios where it becomes necessary to change one data type to another, with converting a string to an integer being a common requirement in programming tasks.
For instance, consider a numeric string like " 143 " that needs to be converted to a numeric data type. In this scenario, a specific function is required to transform the string into an integer, resulting in the numeric value 143. Moving forward, we will delve into various techniques within the C++ programming language that facilitate the conversion of string data into integers.
Different methods to convert the string data into integers in the C++ programming language.
- Using the stringstream class
- Using the stoi function
- Using the atoi function
- Using the sscanf function
Using the stringstream class
The stringstream class is employed for transforming a string containing numerical values into an integer data type. This class defines a stream object for inserting a string and retrieving the integer data through stream operations. Within the stringstream class, "<<" and ">>" operators are utilized to extract data from the (<<) operator and insert data by passing stream to (>>) left operand.
Let's develop a program to showcase the stringstream class for converting string data into an integer in the C++ programming language.
Program1.cpp
#include <iostream>
#include <sstream> // use stringstream class
using namespace std;
int main()
{
string str1 = "143"; // declare a string
int intdata; // declare integer variable
/* use stringstream class to declare a stream object to insert a string and then fetch as integer type data. */
stringstream obj;
obj << str1; // insert data into obj
obj >> intdata; // fetch integer type data
cout << " The string value is: " << str1 << endl;
cout << " The representation of the string to integer type data is: " << intdata << endl;
return 0;
}
Output
The string value is: 143
The representation of the string to integer type data is: 143
In the preceding code snippet, we employ the stringstream class to instantiate an obj object, facilitating the conversion of string data to an integer. Subsequently, we utilize the ">>" operator to retrieve the converted string from obj and convert it into numerical data.
Using the sscanf function
The sscanf function transforms a provided string into a specific data type such as an integer.
Syntax
sccanf ( str, %d, &intvar);
The sscanf function requires three parameters - the character string (str), format specifier (%d), and the integer variable (&intvar) to hold the converted value.
Algorithm of the sscanf function
- The sscanf function belongs to the stringstream class, so we need to import the class into our program.
- Initialize a constant character string str.
- Create an integer variable to hold the converted string to integer values.
- Pass the string variable into the sscanf function, and assign the sscanf function to the integer variable to store the integer value generated by the function.
- Print the integer values.
Let's explore an example where we can utilize the sscanf function to convert a string into a numerical value in the C++ programming language.
Program2.cpp
#include <iostream>
#include <sstream> // use stringstream class
using namespace std;
int main ()
{
// declare the character strings
const char *str1 = "555";
const char *str2 = "143";
const char *str3 = "101";
// declare the integer variables
int numdata1;
int numdata2;
int numdata3;
/* use sscanf() function and to pass the character string str1,
and an integer variable to hold the string. */
sscanf (str1, "%d", &numdata1);
cout <<" The value of the character string is: " << str1;
cout << "\n The representation of string to int value of numdata1 is: " << numdata1 <<endl;
sscanf (str2, "%d", &numdata2);
cout <<"\n The value of the character string is: " << str2;
cout << "\n The representation of string to int value of numdata2 is: " << numdata2 <<endl;
sscanf (str3, "%d", &numdata3);
cout <<"\n The value of the character string is: " << str3;
cout << "\n The representation of string to int value of numdata3 is: " << numdata3 <<endl;
return 0;
}
Output
The value of the character string is: 555
The representation of string to int value of numdata is: 555
The value of the character string is: 143
The representation of string to int value of numdata is: 143
The value of the character string is: 101
The representation of string to int value of numdata is: 101
Using the stoi function
The stoi function converts a string value into an integer data type by accepting the string as an argument and providing an integer output.
Syntax
stoi(str);
The stoi function takes a str parameter, which is the string input provided to stoi for the conversion of string data to an integer value.
Algorithm of the stoi function
- Initialize the string variable to store string values.
- After that, it creates an integer type variable that stores the conversion of string into integer type data using the stoi function.
- Print the integer variable value.
Let's develop a script that utilizes the stoi method for converting string values to integers within the C++ coding language.
Program3.cpp
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string strdata1 = "108";
string strdata2 = "56.78";
string strdata3 = "578 Welcome";
// use stoi() function to pass string as arguments
int intdata1 = stoi (strdata1);
int intdata2 = stoi (strdata2);
int intdata3 = stoi (strdata3);
// print the converted values
cout << " The conversion of string to an integer using stoi(\"" << strdata1 << "\") is " << intdata1 <<endl;
cout << " The conversion of string to an integer using stoi(\"" << strdata2 << "\") is " << intdata2 <<endl;
cout << " The conversion of string to an integer using stoi(\"" << strdata3 << "\") is " << intdata3 <<endl;
return 0;
}
Output
The conversion of string to an integer using stoi("108") is 108
The conversion of string to an integer using stoi("56.78") is 56
The conversion of string to an integer using stoi("578 Welcome") is 578
Using the atoi function
A function atoi is employed to transform a character string into an integer value. It accepts a string of characters as input and outputs an integer value.
Syntax
atoi (const char *str);
Algorithm of the atoi function
- Initialize a pointer-type character array to store a string.
- After that, it creates an integer type variable that stores the conversion of string into integer type data using the atoi function.
- Print the integer variable value.
Let's develop a program that utilizes the atoi function to transform a string value into an integer data type within the C++ programming language.
Program4.cpp
#include <iostream>
#include <string>
using namespace std;
int main ()
{
// declare a constant character array of string
const char *strdata1 = "256";
const char *strdata2 = "16.18";
const char *strdata3 = "1088 Good Bye";
// use atoi() function to pass character type array as arguments
int intdata1 = atoi (strdata1);
int intdata2 = atoi (strdata2);
int intdata3 = atoi (strdata3);
// print the converted values
cout << " The conversion of string to an integer value using atoi(\"" << strdata1 << "\") is " << intdata1 <<endl;
cout << " The conversion of string to an integer value using atoi(\"" << strdata2 << "\") is " << intdata2 <<endl;
cout << " The conversion of string to an integer value using atoi(\"" << strdata3 << "\") is " << intdata3 <<endl;
return 0;
}
Output
The conversion of string to an integer value using atoi("256") is 256
The conversion of string to an integer value using atoi("16.18") is 16
The conversion of string to an integer value using atoi("1088 Good Bye") is 1088
