Output of If-else ladder not functioning

For some reason the output will not print the any charge. I don't understand why. I know its a stupid little error, but I am a stupid little programmer. :^)

Code:

#include <iostream.h>
#include <iomanip.h>
#include <windows.h>
#include <math.h>

void input(int &group, double &time);
void computation(int &group, double &time, double &charge);
void output(int &group, double &time, double &charge);

int main()
{
	int group; // type of vehical array
	double time; // time in lot variable
	double charge; // charge variable
	
	input(group, time);	
	
	computation(group, time, charge);
	
	output(group, time, charge);
	
	return 0;
}

// definition of input function

void input(int &group, double &time)
{
	cout << "Please enter the type of vehical to be charged." << endl;
	do
	{
		cout << "(Enter 1 for Car, 2 for Truck, or 3 for Senior Citizen)" << endl;
		cin >> group;
		
		if(group != 1 && group != 2 && group != 3)
		{
			cout << "Please enter a correct charge group";
		}
	}
	while(group != 1 && group != 2 && group != 3);
	
	do
	{
		cout << "Please enter the length of time stayed." << endl;
		cin >> time;
		
		if(time <= 0)
		{
			cout << "Please enter a positive time";
		}
	} while(time <= 0);
	
}

// definition of computation function

void computation(int &group, double &time, double &charge)
{
	if(group == 1)
	{
		if(time > 5)
		{
			charge = (time - 5) * .25 + 2; 
		}
		else if(time > 1)
		{
			charge = (time - 1) * .5; 
		}
	}
	
	if(group == 2)
	{
		if(time > 6)
		{
			charge = (time - 6) * .75 + 4;
		}
		else if(time > 2)
		{
			charge = time - 2;
		}
	}
	else
	{
		charge = 0;
	}
}

// definition of output function

void output(int &group, double &time, double &charge)
{
	cout << endl << "Parking Lot Bill" << endl;
	if(group == 1)
	{
		cout << "Charge Group: "<< "Car" << endl;
	}
	else if(group == 2)
	{
		cout << "Charge Group: " << "Truck"  << endl;
	}
	else if(group == 3)
	{
		cout << "Charge Group: " << "Senior Citizen"  << endl;
	}
	cout << "Time In Lot : " << time << " Hours" << endl;
	
	if(charge = 0)
	{
		cout << "Total Charge: " << "No Charge" << endl;
	}
	
	if(charge != 0) 
	{
		cout << "Total Charge: $" << charge << endl;
	}
	cout << endl << "Thank You, Have A Nice Day" << endl;
}

Code:

if(charge == 0)

if(charge != 0)

Is also redundent. You check, (or will be checking), to see if it is equal to zero, so all you need is an else there.