A postfix calculator!!...but somewhat broken

Good day to you.... I have this problem with my postfix calc.. I suspect it doesnt calculate at all ! .. it only writes input ...maybe theres error in string conversion.. please help if you can

Code:

#include <iostream>
#include <math.h>
#include <string.h>

bool err = false;	
//stack : 
const int SIZE = 100;
double stack[SIZE]; 
int nOperandu = 0; 

bool push(double x)
{
	if (nOperandu<SIZE)
	{
		stack[nOperandu++] = x;
		return true;
	}
	return false;
}

bool pop(double &x)
{
	if (nOperandu>0)
	{
		x = stack[--nOperandu];
		return true;
	}
	return false;
}

int getCount()
{
	return nOperandu;
}

bool isEmpty()
{
	return nOperandu==0;
}

//end of stack

// functions: 
void add() 
{
	double a;
	double b;
	pop(b);		 
	pop(a);

	push(a+b);
}
void minus() 
{
	double a;
	double b;
	pop(b);		 
	pop(a);

	push(a-b);
}
void multiply() 
{
	double a;
	double b;
	pop(b);		 
	pop(a);

	push(a*b);
}
void divi() 
{
	double a;
	double b;
	pop(b);		 
	pop(a);
	if (b == 0)
		{
			printf("Cant div. by 0.\n");
			err = true;
		}
	else push(a/b);
}
void mod()
{
	double a;
	double b;
	pop(b);		
	pop(a);
	if (b == 0)
		{
			printf("Cant div. by 0.\n");
			err = true;
		}
	else push(a / b);
}

void powa() 
{
	double a;
	double b;
	pop(b);		
	pop(a);
	if ((a == 0) && (b < 0)) 
		{
			printf("Cant pow. with negative number.\n");
			err = true;  
		}
	else push(pow(a,b));
}
void full() 
{
	double a;
	pop(a);

	if (a < 0) push(ceil(a));
		else push(floor(a));
}			

// end of functions

// main alg: 
void alg()
{
	char line[256];
	char *cast = NULL;
	char *nextCast = NULL;
	double result;

	printf("Add numbers in postfix:\n ");
	gets_s(line,255);	// loads line
	cast = strtok_s(line," \n", &nextCast); 
	while ((cast != NULL) && !(err)) // loop till error 
        {
		if ((cast[0]!='+') || (cast[0]!='-') || (cast[0]!='*') ||
		    (cast[0]!='/') || (cast[0]!='%') || (cast[0]!='^') ||
		    (cast[0]!='f'))  // if first char isnt operator then convert to number and add to stack  
		{
			push(atof(cast));
		}
		else
		{
			switch (cast[0]) // chceks if there are enough operands in cases
			{
				case '+': 
					if (getCount() >= 2) add(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case '-': 
					if (getCount() >= 2) minus(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case '*': 
					if (getCount() >= 2) multiply(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case '/': 
					if (getCount() >= 2) divi(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case '%': 
					if (getCount() >= 2) mod(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case '^': 
					if (getCount() >= 2) powa(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
				case 'f': 
					if (getCount() >= 1) full(); 
						else 
						{
							printf("Not enough operators.\n");
							err = true; 
						}
					break;
			}
		}
        	cast = strtok_s( NULL, " \n", &nextCast); // jumps to next part of the line
    	}
	/*
	if (isEmpty()) printf("Lack of operators\n"); 
	else
	if (getCount() > 1) printf("Too many operators\n"); 
	else*/
	if (!err)
	{
		pop(result);
		printf("Result is: %0.5lf.\n",result); // writes result with 5 decimal
	}
}
//and of alg
int main()
{
	alg();
	//return 0;
	system("PAUSE");
}