Input Validation

[Undefined95]

I'm supposed to reproduce the function isValidInt to validate the format for
an integer which has been entered using the keyboard.

Test your function using the following test cases:

-1234
5674.25
$1700
Here's my code:

  #include <iostream>
#include <string>
#include <sstream>

using namespace std;

string value;
int number;

int main()
{
cout << "Enter an integer: ";
  getline(cin, value);

bool isvalidInt( string str )
{
     int start = 0;          //start position in the string
     int i;                    //   position in the string         
     bool valid = true;    //assume a valid integer 
     bool sign = false;    //assume no sign 

    //check for an empty string
	if (str.length() == 0)    valid = false;

//Check the first character
if( valid )           
       // check for a leading sign
        if ( str.at(0) == '-'|| str.at(0) == '+' ) 
        { 
	         sign = true;
	         start = 1;              // start checking for digits after the sign
            //check that there is at least one character after the sign
            if ( sign && str.length() == 1 )
                  valid = false;
        }
        else if(  ! isdigit( str.at(0) )   )        // is it a non-digit character 
               valid = false;
               
               
//now we can check the string for all digits, 
//which we know has at least one non-sign char
     i = start;

     //we have checked  i  number of chars so far
     while( valid  &&  i != str.length() )
     {
         if(  ! isdigit(str.at(i))  ) 
                valid = false;          //found a non-digit character

	    i++;                               // move to next character
     }

    if ( ! isValidInt(value) )
       cout << "The value you entered is not a valid integer.\n\n";
  else
  {
      number = atoi(value.c_str());
  }   
   return valid;

Can someone please explain what I'm doing wrong?

[JewelCpp]

function definitions must be outside of functions (including main function)

by the way where does isvalidInt end?
if like I'm guessing at line 59 you should put a closing } after it
and outside of the function it isn't called so all your hard-work won't get executed at all

[Undefined95]

Can you explain what you mean by "

and outside of the function it isn't called so all your hard-work won't get executed at all

"?