CareerCup

/* Return value:
integer value of the string passed

Functionality:
Below function works for examples as shown below:
"0" -> output = 0
"1" -> output = 1
"123" -> output = 123
"-1" -> output = -1
"+1" -> output = 1
" 0" -> output = 0
" -1" -> output = -1
" +1" -> output = 1
"00" -> output = 0
"-01" -> output = -1
"+01" -> output = 1
"00123" -> output = 123
"12300" -> output = 12300
" -0123" -> output = -123
" +0123" -> output = 123
"*123" -> output = 123
"123*" -> output = 123
"*123*" -> output = 123
"*-123" -> output = -123
“*+123” -> output = 123
“123-“ -> output = 123
“123+” -> output = 123
"*12*3" -> illegal input -> undefined output = 12
"*-*12" -> illegal input -> undefined output = 0

Algorithm:
1. Skip any non digit characters, which are not '-'
2. If you hit a '-', it means its a negative number. Skip '-' and make
is_negative boolean true.
3. From this point, while you have continuous digits, do
a. Every iteration of the digit, multiply the int_val by 10 and add (digit value%10)
4. If is_negative is true, multiply the int_val by -1 and return,
else return int_val */
int atoi(char *str)
{
int is_negative = 0;
int int_val = 0;

/* Skip non digit characters excluding '-' */
while (!isdigit(*str) && (*str != '-'))
{
str++;
}
/* Number is negative */
if (*str == '-')
{
is_negative = 1;
str++;
}

/* Compute the int_val for contiguous digits */
while (isdigit(*str))
{
int_val = (int_val*10) + (*str - '0')%10;
str++;
}
return ((is_negative) ? (int_val * -1): int_val);
}

It will die if input string is "asfbsdf" so little modification...
while (!isdigit(*str) && (*str != '-'))
{
str++;
}
should be ...
while (!isdigit(*str) && (*str != '-'))
{
if(*str=='\0')
{
printf("undefined output");
return o;
}
str++;
}

Similar checks for '\0' should be present in other parts as well!

Kewl solution. I like that int_val = (int_val*10) + (*str - '0')%10; It is very cryptic and really nice.

Here is a similar solution...just a different framework.

#include <iostream.h>
long Atoi(const char*);
int main(void)
{
while(1)
{
char s[20];
cout<<"Enter string to convert to integer (q to quit): ";
cin>>s;
if(!strcmp(s,"q")) break;
cout<<"Standard atoi function's output: "<<atoi(s)<<endl;
cout<<"Custom made Atoi function's output: "<<Atoi(s)<<endl;
}
}
long Atoi(const char *str)
{
short negative = 1;
long intVal=0;
if(str[0] == '-')
{
negative = -1;
str++;
}
else if(str[0] == '+')
str++;
while(*str >= '0' && *str++ <= '9')
intVal = intVal*10 + (*(str-1)-'0');
return negative*intVal;
}

"It is very cryptic and really nice."

ha ha ha...

bool bIsNav=false;
int iRet;

if(*chr='-')
{
bIsNav=true;
chr++;
}
else if(*chr=='+')
{
chr++;
}

while (chr!=null)
{
if(*chr>='0'&&*chr!='9')
{
iRet=iRet*10+(*chr);
}
else
{
system.out("this is not a integer");
}

if (bIsNav)
return -iRet
else
return iRet;
}

/* with minimal error checking

unsigned int atoi(char* number) {

if (number == NULL || strcmp(number,"") == 0) {
return 0;
}

unsigned int iNumber = 0;

while (number != NULL && strcmp(number,"") != 0) {
if(*number <= '9' && *number >= '0' ) {
iNumber = (iNumber << 3) + (iNumber << 1)+(*number++ - '0');
}
else {
return 0;
}
}

return iNumber;
}

#include <stdio.h>
#include <string.h>
#include <math.h>

unsigned int atoi(char* number);

int main() {
int number;

number = atoi("35.223");
printf("Number is %d\n",number);


return 0;
}


int atoi(char* number) {
int iNumber = 0; //initialize it to 0
int loopIndex;//index that loops through the number string
int strLen = 0;
char *decimalPoint;

if(number != NULL) { //string points to a null character
if(strcmp(number, "") != 0) {//check if the string is not empty
strLen = strlen(number);
if(strchr(number, '.') != NULL) {
decimalPoint = strrchr(number, '.'); //Truncate the digits after the decimal point
strLen = decimalPoint-number;
}

if(number != NULL) {
for(loopIndex = strLen-1; loopIndex >= 0; loopIndex--) {
if(number[loopIndex] <= '9' || number[loopIndex] >= '0') {
iNumber+=(pow(10, ((strLen-1)-loopIndex)))*(number[loopIndex]-'0');
}
}
}
}
}
return iNumber;
}

uint atoi(char* str)
{
if (!s ) return 0;
int sum = 0;
int mult = 0;
int sign = 1;

if (*s == '-')
{
++s;
sign = -1;
}

while (*s)
{
if (*s <= '0' && *s >= 9) break;
sum = sum*mult + (*s - '0');
++s;
mult *= 10;
}

sum *= sign;

return sum;
}

return int and not uint as we are taking care of '-' sign in above program. the earlier post is taking care of decimal. that would be dtoi and not atoi. and we should be using strcmp and strlen etc which are single pass over string.

I think there is one problem in vivek code:

sum = sum*mult + (*s - '0');

should be:

sum = sum*10 + (*s - '0');

and remove all "mult" from the code.

int sum=0;
int mult=1;

int start= first(s,'.'); // find first occurance of .
if (start==-1) start=strlen(s)-1; // no ., start at end

for ( i=start; i>=0 ; i--) {
int v= (s[i]-'0') * mult;
sum = sum + v;
}

// yeah, I assume ascii - it wont work with ebcdic or other character sets with holes
// yea, I assume no commas.
// yeah, I didn't write first()... most langs have such a fuction to find the first occurance of a character in a string

int sum=0;
int mult=1;

int start= first(s,'.'); // find first occurance of .
start--;
if (start < 0 ) start=strlen(s)-1; // no ., start at end

for ( i=start; i>=0 ; i--) {
int v= (s[i]-'0') * mult;
sum = sum + v;
}

// yeah, I assume ascii - it wont work with ebcdic or other character sets with holes
// yea, I assume no commas.
// yeah, I didn't write first()... most langs have such a fuction to find the first occurance of a character in a string

#include<stdio.h>
#include<limits.h>

typedef enum {
WHITE_SPACE,
GETDIGITS,
FINISHED
} get_state;

typedef enum {
POSITIVE,
NEGATIVE
} get_sign;


int get_int(char * ch){

get_state state = WHITE_SPACE;
get_sign sign = POSITIVE;


int value = 0;
int limit = INT_MAX / 10;


int dig;


if(*ch){
while(state != FINISHED){
dig = (unsigned int)*ch++;

switch(state){

case WHITE_SPACE:
if(dig == ' '){
;
}

else if(dig == '+'){
state = GETDIGITS;
}

else if(dig == '-'){
state = GETDIGITS;
sign = NEGATIVE;
}
else if(dig >= '0' && dig <= '9'){
value = dig - '0';
state = GETDIGITS;
}
else{
state=FINISHED;
}

break;

case GETDIGITS:
dig = dig - '0';
if( !( ( dig >= 0 ) && ( dig <= 9 ) ) ){
state=FINISHED;
break;
}

if( value < limit ||
( (value ==limit) &&
(((sign == POSITIVE) && (INT_MAX - value * 10 >= dig))
|| ((sign == NEGATIVE) && (- INT_MIN - value * 10 >= dig)))) ){
value = value * 10 + dig ;
}
else{
if(sign == NEGATIVE)
value=INT_MIN;
else
value=INT_MAX;

state=FINISHED;
}
break;

case FINISHED:

default:
break;

}
}

}
if( sign == NEGATIVE )
value = value * -1;

return value;

}

int main(){

char str[20];

while(1){

printf("\nEnter Number: ");

fgets(str , sizeof(str),stdin);

fflush(stdin);

printf("\nYou Entered = %d ",get_int(str));
}

}

Here is my code...

#include<stdio.h>
void main()
{
	char str[100];
	char * ptr;
	printf("Enter the string \n");
	ptr = gets(str);
	int i =0;
	int val = 0;
	while(str[i]!='\0' && (str[i] >='0' && str[i] <='9' || str[i] == '-'))
	{
		if(str[i] == '-')
		{
			i++;
			continue;
		}
		val = str[i]-'0' + val*10;
		i++;
	}
	if(str[0] == '-')
		printf("The value is %d \n",0- val);
	else
		printf("The value is %d \n", val);
}

here's my method:

1) kick out all characters which is not '+','-','0'-'9', make a new string;
2) in the new string, if '+','-' does not occur at first place, illegal;
3) other wise, generate the number of "pure-digits" number and add with the corresponding sign.

int myatoi(const char* ptr)
{
int n = 0;
for(; *ptr <= '9' && *ptr >= '0'; ptr++)
{
n = n * 10 + (*ptr - '0');
}

return n;
}

example atoi('10', 2) returns 2 in decimal