help with find_if

**cdkiller** · 10-01-2006

In a previous post somebody, i can't remember their name, told me to use find_if. well i decided to use find_if for something else but i cant seem to get it to loop. i built it to validate numbers, at present it does what i want but it only does it once. here is the code.

Code:

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <cctype>


using std::cin;
using std::cout;
using std::string;
using std::endl;
using std::find_if;

bool digi (char p)
{
	if (! isdigit(p))
		return true;
	else 
		return false;
}

int main()
{
	string test;
	do {
	std::getline(cin, test);
	if(find_if(test.begin(), test.end(), digi)==test.end())
	
		cout << "good";
	
	else 
		cout<< "bad";
	} while (!digi);
	
	return 0;
}

i have to validate integer inputs in more than one instance so i also want to make the entire validation code into a function but i will try that after i get it working here. i have a feeling that my problem is the

Code:

 while (!digi);

but i dont know what else to put, lol. please forgive the messy code, testing phase is always messy for me.

**laserlight** · 10-01-2006

You dont need the do while loop at all. find_if() iterates over the string for you.

**cdkiller** · 10-01-2006

Thanks but thats not the problem, sorry if i did not come out clearly. what i really want is for it to keep prompting for input once the current input is bad. currently if i input a letter for example it just outputs "bad" and it finishes. but what i want is for it to say "bad" and then prompt again for input until a good input is given.

**laserlight** · 10-01-2006

In this case, it may be better to use std::string::find_first_not_of() instead of the more general std::find_if() algorithm.

Code:

do {
    std::cout << "Enter an integer: ";
    std::getline(std::cin, test);
} while (test.find_first_not_of("0123456789", 0) != std::string::npos);

**cdkiller** · 10-01-2006

thanks that works. since its so short i wont bother to make it into a function. i tried to functionify it once before with my own code and it worked for valid numbers but when i entered an invalid number it stuck in an infinite loop. my piece of code was much longer though. thats why i tried using the bool function instead. i will stick with what you gave me.

moving along, could you explain in simpleton language what the last zero before the ) represents in the last line of code?

Code:

 while (test.find_first_not_of("0123456789", 0) != std::string::npos);

also i was wondering how to call a function from another funtion? like in the following simple attempt.

Code:

 #include <iostream>
using namespace std;

int addition (int a, int b)
{
  int r;
  r=multiply(a,b) + a;
  return (r);
}

int multiply (int c, int d)
{
  int y = c+d;
	return (y);
}

int main ()
{
  int z;
  z = addition (5,3);
  cout << "The result is " << z;
  return 0;
}

i know it dont make sence mathematically, lol but i was trying something simple to help me undertsand it easier. now that gives me an error multiply identifier not found. what i am attempting to do is use the multiply function in the addition function.

**laserlight** · 10-01-2006

moving along, could you explain in simpleton language what the last zero before the ) represents in the last line of code?

Just read about find_first_not_of().

As for your next problem, you can solve it by:
a) defining multiply() before addition(), or
b) place a function prototype for multiply() before addition()

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