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atoi() Function with Example in C++

C++ atoi() function: Here, we are going to learn about the atoi() function with example of cstdlib header in C++ programming language.
Submitted by IncludeHelp, on May 26, 2020

C++ atoi() function

atoi() function is a library function of cstdlib header. It is used to convert the given string value to the integer value. It accepts a string containing an integer (integral) number and returns its integer value.

Syntax of atoi() function:

C++11:

    int atoi (const char * str);

Parameter(s):

str – represents a string containing an integer (integral) number.

Return value:

The return type of this function is int, it returns the integer converted value.

Example:

    Input:
    str = "123";

    Function call:
    atoi(str);

    Output:
    123

C++ code to demonstrate the example of atoi() function

// C++ code to demonstrate the example of
// atoi() function

#include <iostream>
#include <cstdlib>
#include <string.h>
using namespace std;

// main() section
int main()
{
    char str[50];

    strcpy(str, "123");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    strcpy(str, "-123");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    strcpy(str, "0");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    strcpy(str, "1234567");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    strcpy(str, "12345678");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    strcpy(str, "-12345678");
    cout << "atoi(\"" << str << "\"): " << atoi(str) << endl;

    return 0;
}

Output

atoi("123"): 123
atoi("-123"): -123
atoi("0"): 0
atoi("1234567"): 1234567
atoi("12345678"): 12345678
atoi("-12345678"): -12345678