CareerCup

bool isNumber(char *str)
{

 trim(str); // remove leading and trailing spaces.
  
  int i=0; 
  bool dec=false; //is decimal?
  while(str[i])
  {
    if(str[i] == '-' || str[i] == '+'){
       if(i!=0) return false;
    }
   else if(str[i] == '.'){
     if(dec) 
        return false; //we can have only one decimal point in a number
     else 
        dec = true;
   
     if(!str[i+1])  // make sure decimal is not last char in the string
        return false; 
   }
   else if(str[i] <= '0' || str[i]>='9') return false;
   i++;
  }
}

<pre lang="" line="1" title="CodeMonkey52161" class="run-this">/* Assuming the string is ascii and would denote only +ve numbers.
If negative numbers are allowed, we'd need an additional step to check if first character of the string is a '-' */
class NumCheck{
public static boolean isNumber(String str)
{
boolean isNum=true;
for (int i = 0; i < str.length(); i++){
char c = str.charAt(i);
if(!(c>47 && c<58)) //checking if it lies in the ascii range for numbers
{
isNum= false;
break;
}
}
return isNum;
}
public static void main(String[] args)
{
System.out.println(isNumber("256")?"yes":"no");
System.out.println(isNumber("2fifty6")?"yes":"no");
}
}
</pre><pre title="CodeMonkey52161" input="yes">
</pre>

return inputString,matches("[+-]?//d+(.//d+)?");

What type of number? if a string is Integer or if a string is a Double

ASCII comes to rescue here !!

Iterate over the characters and check if the ascii is between 48 and 57. Its a number.

Negative numbers were not considered here

This is very tedious. On an interview, the interviewer is looking to test your carefulness, etc.

A pretty good solution over here h t t p ://rosettacode.org/wiki/Determine_if_a_string_is_numeric

i=0;
while(ar[i] >= '0' && ar[i] <= '9')
i++;
check if i is last character or not.

boolean isNumber = false;
try {
  Double.parseDouble(inputStr)
isNumber = true;
} catch (NumberFormatException e) {

}

bool validateNum(string in)
{
    bool decimalFound = false, numFound = false;
    int i=-1;

    if(in[0]=='+' || in[0]=='-') i = 1;
    else i=0;

    for(; i<in.length(); i++)
    {
        switch(in[i])
        {
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9': numFound = true;
                      break;
            case '.':
                      if(decimalFound) return false;
                      else if(numFound) decimalFound = true;
                      else return false;
                      break;
            default:
                        return false;
        }
    }
    return true;
}

Using explicit state variable makes it easier to extend the syntax covered.
This program covers octal, decimal, and hex integer numbers and both decimal and hex floating point number (without exponent).

#include <iostream>
#include <sstream>
#include <iomanip>

using namespace std;

enum State {
	s_start,
	s_sign,
	s_0,
	s_0x,
	s_octal,
	s_decimal,
	s_hex,
	s_decdot,
	s_hexdot,
	s_nan,
};

bool isNumber(string & str)
{
	State state = s_start;

	for (int i = 0; i < str.length(); i++) {
		char c = str[i];
		State next_state = s_nan;

		switch(state) {
		case s_start:
			if (('+' == c) || ('-' == c)) {
				next_state = s_sign;
			} else if ('0' == c) {
				next_state = s_0;
			} else if (('1' <= c) && (c <= '9')) {
				next_state = s_decimal;
			}
			break;

		case s_sign:
			if ('0' == c) {
				next_state = s_octal;
			} else if (('1' <= c) && (c <= '9')) {
				next_state = s_decimal;
			}
			break;

		case s_0:
			if (('x' == c) || ('X' == c)) {
				next_state = s_0x;
			} else if (('0' <= c) && (c <= '7')) {
				next_state = s_octal;
			} else if ('.' == c) {
				next_state = s_decdot;
			}
			break;

		case s_octal:
			if (('0' <= c) && (c <= '7')) {
				next_state = s_octal;
			}
			break;

		case s_decimal:
			if ('.' == c) {
				next_state = s_decdot;
				break;
			}
			// Fallthrough
		case s_decdot:
			if (('0' <= c) && (c <= '9')) {
				next_state = s_decimal;
			}
			break;

		case s_hex:
			if ('.' == c) {
				next_state = s_hexdot;
				break;
			}
			// Fallthrough 
		case s_hexdot:
		case s_0x:
			if ((('0' <= c) && (c <= '9'))
				|| (('a' <= c) && (c <= 'f'))
				|| (('A' <= c) && (c <= 'F'))) {
				next_state = s_hex;
			}
			break;

		case s_nan:
			return false;
		}

		state = next_state;
	}

    if ((s_octal == state) || (s_decimal == state) || (s_hex == state) || (s_0 == state)) {
		return true;
	}

	return false;
}
	

#include <cstdlib>

int main(int argc, char *argv[])
{
	const char *s = "";

	if (argc > 1) {
		s = argv[1];
	}

	string str(s);
	bool isanum = isNumber(str);
	cout << "'" << str << "'" << " is" << (isanum ? "" : " not") << " a number" << endl;

	return (0);
}

public static boolean isNumeric(String inputData) {
 
  
  return inputData.matches("[-+]?[0-9]+([.][0-9])?");
}

bool isNumber(char *s) {
     if (s == NULL || *s == '\0')
        return 0;
    char * p;
    strtod (s, &p);
    // cout<<p<<endl;
    if(!strcmp(s," ")) 
        return false;
    if(*p==' '){
        // cout<<"if\n";
        while(*p==' ')
            p++;
    }
    // cout<<strlen(p)<<endl;
    return (*p == '\0' || !strlen(p)>0);
}