Header File 

stdlib.h  

Category 

Conversion Routines, Math Routines 

Prototype 

int atoi(const char *s); 

int _wtoi(const wchar_t *s); 

Description 

Converts a string to an integer.

• atoi converts a string pointed to by s to int; atoi recognizes (in the following order)
• An optional string of tabs and spaces
• An optional sign
• A string of digits

[ws] [sn] [ddd] 

In this function, the first unrecognized character ends the conversion. There are no provisions for overflow in atoi (results are undefined). 

Return Value 

atoi returns the converted value of the input string. If the string cannot be converted to a number of the corresponding type (int), atoi returns 0. 

Example  

 #include <stdlib.h>
 #include <stdio.h>
 int main(void)
 {
    int n;
    char *str = "12345.67";
    n = atoi(str);
    printf("string = %s integer = %d\n", str, n);
    return 0;
 }

Portability