C program for User defined Custom atoi Function Code

/*

C program: atoi function custom

Description: atoi function convert string to integer representation of integral numbers.



Example 1: string "02302"    converts to number 2302

Example 2: string "abcd"     returns 0

Example 3: string "-0234"    converts to number -234

Example 4: string "0023ABCD" converts to number 23

Example 5: string "12abc45g" converts to number 12

Example 6: string "--0123"   returns 0

Example 7: string "" (NULL)  returns 0

Example 8: string "   234a"  converts to number 234

Example 9: string "+  239b"  returns 0

Example10: string "+239"     converts to number 239

Example11: string "   +12"   converts to number 12

Example12: string "   -12"   converts to number -12



Compiler: Turbo C++ 3.0

Author: Mangilal Sharma

Date: September 12, 2015

Program for: world-of-c-programming.blogpost.com

Program number: 102

*/



#include<stdio.h> //for printf and gets

#include<conio.h> //for clrscr and getch

#include<string.h> //for strcpy

typedef enum {false, true} bool; //To use bool data type



bool isNotNumericChar(char x) //to check the character

{

 return(x >= '0' && x<= '9')? false:true;

}



int myAtoi(char *str) //Cutom atoi function code

{

 int result = 0; //Initialize result variable

 int sign = 1; //Initialize sign as positive

 int i = 0; //index of first digit in string



 if(str == NULL) return 0;



 //If number is negative, then update sign

 while(str[i] == ' ') i++;



 if(str[i] == '-')

 {

  sign = -1;

  i++;

 }

 else if(str[i] == '+')

 {

  i++;

 }



 //Iterate through all digits of input string and update result value

 for(;str[i]!= '\0';i++)

 {

  if(isNotNumericChar(str[i])) break; //Break when non numeric char occurs

  //We can also use isdigit function from ctype.h instead of our custom function

  result = result*10 + str[i] - '0';

  //subtracted ASCII value of zero from ASCII value of current digit character

 }



 return sign*result;

}



int main()

{

 char string[] = "02302";

 int val = myAtoi(string);

 clrscr();

 printf("String value = %s, Int value = %d\n",string,val);

 strcpy(string,"C Program");

 val = myAtoi(string);

 printf("String value = %s, Int value = %d\n",string,val);



 printf("Press y for try your strings to atoi function.\n");

 printf("Press any other key to exit.\n");

 while(getch() == 'y')

 {

  printf("Enter String and press enter:");

  gets(string);

  printf("String value = %s, Int value = %d\n",string,myAtoi(string));

 }

 return 1;

}