Population program in C++ - c++

Question

I'm in desperate need of assistance.
I'm working on a population program in C++ for my Systems Software class.
This is my first foray into C++ territory, I only have some Java knowledge to help me out.
Basically, the program is supposed simulate a simple population. The guidelines are as follows:
The first elements (starting population) have random age and sex.
2 elements can pair if their lifespan falls between [0.25,0.50] (assuming they die at 1) and they are of the opposite sex.
Each element can only pair twice.
So here's my code, and take it easy guys I'm not very well versed in C++ yet...:
#include <vector>
#include <ctime>
#include <stdlib.h>
#include <iostream>
#include <iterator>
using namespace std;
class Element {
public:
int pair;
double life;
int tag;
void setValues(double, int);
int getPair() {
return pair;
}
void incrementPair() {
pair = pair++;
}
double getLife() {
return life;
}
void incrementLife() {
life = life + 0.05;
}
int getTag() {
return tag;
}
}; //Element
void Element::setValues(double b, int c) {
pair = 0;
life = b;
tag = c;
}
int main() {
double Time = 0.0;
srand(time(NULL));
vector<Element> vec;
for (int i = 0; i<50; ++i) {
Element x;
x.setValues(((double) rand() / (RAND_MAX)), rand()%2);
vec.push_back(x);
}//for
while (vec.size() != 0) {
int newPopCount = 0;
int Dead = 0;
for(int count = 0; count != vec.size(); ) {
std::vector<Element>::iterator p = vec.begin();
std::vector<Element>::iterator i = vec.begin() + 1;
if ((p->getPair() == 2) || (p->getLife() < 0.25) || (p->getLife() > 0.50)) {
count++;
p++;
}//if
else {
for(int count1 = count + 1 ; count1 != vec.size() ; ) {
if ((i->getLife() < 0.25) || (i->getLife() > 0.50) || (i->getPair() == 2) || (p->getTag() == i->getTag())) {
++i;
count1++;
}//if
else {
cout << i->getTag() << " " << p->getTag() << endl;
cout << i->getPair() << " " << p->getPair() << endl;
cout << i->getLife() << " " << p->getLife() << endl;
p->incrementPair();
i->incrementPair();
newPopCount++;
count1++;
count++;
p++;
i++;
}//else
}//for
}//else
}//for
Time += 0.05;
for ( vector<Element>::iterator m = vec.begin(); m != vec.end(); ++m ) {
m->incrementLife();
if ( m->getLife() >= 1.00 ) {
Dead++;
//vec.clear();
vec.erase(m);
//vec.shrink_to_fit();
}//if
for (int i = 0; i = newPopCount; i++) {
Element woo;
woo.setValues(0.0, rand()%2);
vec.push_back(woo);
}//for
}//for
cout << "The total number of dead is: " << Dead << endl;
cout << "The total number born is: " << newPopCount << endl;
cout << "Current population is: " << vec.size() << endl;
cout << "Population has survived for: " << Time << endl;
sleep(1);
}//while
cout<< "The populace is now extinct." << endl;
cout<< "The populace survived for: " << Time << endl;
}//main
You can see my silly debugging methods, I was getting a Segmentation Fault error before, but I believe that to be fixed. The issue now is that I'm getting stuck in the loops. The program seems to run almost erratically, and I can't pinpoint the issue any closer than inside of one of the loops.
My Dead integer is incremented and displayed properly, but the newPopCount integer is not, which makes no sense to me.
Also the program never gets out of the while loop, it will continue until it gets stuck in another of the many loops I have.
I have had several other issues, which I've been fixing slowly but surely as you can see by my patchwork code.
Any help at all will be greatly appreciated.

Answer 1

Two obvious issues, which your compiler will warn you about if you turn up your warnings high enough.
First:
void incrementPair() {
pair = pair++;
}
This is undefined behavior. Should be just:
void incrementPair() {
++pair;
}
Second:
for (int i = 0; i = newPopCount; i++) {
Element woo;
woo.setValues(0.0, rand()%2);
vec.push_back(woo);
}
That condition in your for loop is almost certainly wrong. It likely should be i <= newPopcount, or something like that.
As a side note, your setValues() member function looks like it's doing the job that a constructor should be doing.
EDIT: Look here:
for(int count = 0; count != vec.size(); ) {
std::vector<Element>::iterator p = vec.begin();
std::vector<Element>::iterator i = vec.begin() + 1;
Imagine you have a std::vector with only one element in it, and then think about what i is going to represent when you do i->getLife() a few lines later. Just having those definitions inside the for loop looks a bit suspicious in itself, since you increment both p and i during the loop, but you're going to reset them again on every iteration, but it's not all that easy to follow the logic, so perhaps that's what you intended.

Answer 2

vec.erase(m); results in an invalid m. You want to do m = vec.erase(m)