CareerCup

int main()
{
char *ptr = "1234";
int res = 0;
while(*ptr != '\0')
{
res = res*10 + *ptr - '0';
ptr++;
}
printf("%d", res);
return 0;
}

private static int convert(String s) {
		
		int res = 0;
		int i =0;
		boolean isNegative = false;
		if(s.length() ==0 ){
			System.out.println("Invalid string");
			return res;
		}
		if(s.toCharArray()[0] == '-'){
			isNegative = true;
			i++;
		}
		
		for(;i<s.length();i++){
			res = 10*res +Character.getNumericValue(s.toCharArray()[i]);
		}
		if(isNegative){
			res=-res;
		}
		if(res >Integer.MAX_VALUE){
			System.out.println("Bigger than max int val");
			return Integer.MAX_VALUE;
		}
		if(res <Integer.MIN_VALUE){
			System.out.println("smaller than min int val");
			return Integer.MIN_VALUE;
		}
		return res;
	}

this is a classic, with some basic ascii conversion you can do this in one run.

in python:

def get_int_val(word):
	output = 0
	for i in range(0, len(word)):
		mult_val = 10**(len(word) -1 - i)
		x = ord(word[i])-48
		if x >= 0 and x <= 9:
			output += mult_val*x
	return output

this will fill any spots taken up by chars with 0's, it can easily be modified to not do that. The logic is to use the base-10 property of the integer to get properly placed values added to the sum and returned. O(n) time.

class SolutionConvertStringToInteger {
    public void convert(String str) {
        int negFlag = 1;
        int start = 1;
        int out = str.charAt(0) - '0';
        if(str.charAt(0) == 45) {
            negFlag = -1;
            out = str.charAt(1) - '0';
            start = 2;
            if(out < 0 || out > 9) {
                System.out.println("INVALID NUMBER");
                return;
            }
        }
        for(int i = start; i < str.length(); i++) {
            int temp = str.charAt(i) - '0';
            if(temp < 0 || temp > 9) {
                System.out.println("INVALID NUMBER");
                return;
            }
            out = (out * 10) + temp; 
        }
        System.out.println(out * negFlag);
    }
}

public class ConvertStringToInteger {

    public static void main(String[] args) {
        SolutionConvertStringToInteger mSol = new SolutionConvertStringToInteger();
        mSol.convert("67889");
        mSol.convert("-67889");
        mSol.convert("-678-89");
        mSol.convert("678-89");
    }
}

public static Integer convert(String word){
	int index = 0;
	if(0==word.length() )
		return null;
	int num=0;
	boolean isNegative = false;
	char [] chWords = word.toCharArray();
	if(chWords[index]=='-' || chWords[index]=='+'){
		if(chWords[index]=='-')
			isNegative = true;
		index++;
	}
	for(;index < chWords.length; index++){
		if(chWords[index]<'0' || chWords[index]>'9'){
			System.out.println("Invalid input");
			return null;
		}else{
			num=num*10 + chWords[index]-'0' ;
		}
	}
	if(isNegative)
		num *=-1;
	return num;
}

public class GetIntValue{

public static void main(String[] args) {
String a="1233";
System.out.println("integer value " + retunIntValue(a));
}

/** returns the int value */
public static int retunIntValue(String n1) {
int intValue;
intValue =Integer.parseInt(n1);
return min;
}
}

// pStr = "3456"
int	my_atoi(char *pStr)
{
	int val = 0;

	UINT len = strlen(pStr);
	UINT index = 0;
	UCHAR curr_char = 0;
	for (int i = len-1; i >=0; i--) {
		if (pStr[i] == '-') { continue; }
		printf("i is %d\n", i);
		curr_char = pStr[i];
		int curr_val = ((int) curr_char) - '0';
		val += (curr_val * pow(10, index++));
	}
	if (pStr[0] == '-') { val = 0 - val; }
	return(val);
}

class StringToInteger{

static int stringToInteger(String str)
{
char ch=' ';

int no=0,temp=0,len=str.length();

for(int i=0;i<len;i++)
{
ch=str.charAt(i);

if(Character.isDigit(ch))
{
temp=Character.getNumericValue((int)ch);

no=no+temp;
no=no*10;
}
else
{
no=0;
System.out.println("Please enter only numeric values");
System.exit(0);
}
}
no=no/10;
return no;
}

public static void main(String[] args)
{
String str="12a34";

System.out.println("Integer No is: "+stringToInteger(str));
}
}

Integer.parseInt(s, 10);

complex java solution

Integer.parseInt(s, 10);

#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int my_atoi(string str){
  int counter=str.size();
  int ret=0;
  for (unsigned it = 0; it<str.size(); ++it) {
    cout<<str[it]<<endl;
    ret+=pow(10, counter-it-1)*(str[it]-'0');
    cout<<ret<<endl;
  }
  return ret;
}

int main(int argc, char *argv[]) {
  cout<<my_atoi("1234");
}

#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int my_atoi(string str){
  int counter=str.size();
  int ret=0;
  for (unsigned it = 0; it<str.size(); ++it) {
    cout<<str[it]<<endl;
    ret+=pow(10, counter-it-1)*(str[it]-'0');
    cout<<ret<<endl;
  }
  return ret;
}

int main(int argc, char *argv[]) {
  cout<<my_atoi("1234");

}

here is the solution

ConvertToInt(inputStr)
	length <- inputStr.Length
	if length > k  // k is the size of the maximum integer
		Overflow;return;
	multiplier = 1;
	output = 0;
	maxLastNum = r;
	for i = length; j > 1; j --
		output = output*multiplier + Int(inputStr[i]);
		multiplier = multiplier * 10;
	if Int(inputStr[length]) > maxLastNum OR Int(inputStr[length])*multiplier > MaxInt-output
		Overflow;return;
	else
		output = output*multiplier + Int(inputStr[length]);
	return output

private static int ConvertToInt(string input)
        {
            int result = 0;
            int d = 1;
            for(int i=input.Length -1 ; i>=0; i--)
            {
                result +=  (input[i] - '0') * d;
                d = d * 10;
            }
            return result;
        }

int toInt(String str){
    int n = 0;
    
    for (int i = 0; i < str.length(); i++){
        n *= 10;
        n += str.charAt(i) - '0';
    }

    return n;
}