Arduino 8x8 LED matrix won't turn off

Question

So i'm learning how to control an 8x8 LED matrix with an arduino, however for some reason my code isn't working. I've got 8 rows(each attached to it's own pin, from 12 - 5), and 4 columns(each with it's own pin, pins 0-3) working at the moment. I want to make a snake kind of design with my LEDs, so it moves diagonally. the code was working, and then i decided to add two rows of code(which i've deleted now) and it's still not working. What happens is all of the LEDs light up perpetually, instead of one at a time.

EDIT: I know that use of delay is generally not good, as well as the fact i should have used a switch case, but I figured this was simple enough to not have to worry about it.

Here's the code:

int pinnum = 13;
int lastpin = 0;
int col = 0;
int k;

void setup() {  //runs once
//  initialize pins as outputs
  for(int pinnum; pinnum >= lastpin; pinnum--) 
  {
    pinMode(pinnum, OUTPUT);
  }
  for(int i = 5; i <= 13; i++) //starts with all of them off
  {
    digitalWrite(i,LOW);
  }
  for(int i = 0; i <= 4; i++) //starts with all of them off
  {
    digitalWrite(i, HIGH);
  }

}//   END SETUP

void loop() {

 pinon(12);
 togglecol();
 delay(1000);

 pinon(11);
togglecol();
 delay(1000);

 pinon(10);
 togglecol();
 delay(1000);

 pinon(9);
 togglecol();
 delay(1000);

 pinon(8);
 togglecol();
 delay(1000);

 pinon(7);
 togglecol();
 delay(1000);

 pinon(6);
 togglecol();
 delay(1000);

 pinon(5);
 togglecol();
 delay(1000);
}

void togglecol() 
{
 if(col % 4 == 1) //column = 1, pin 3
 {
  digitalWrite(0, HIGH);
  digitalWrite(1, HIGH);
  digitalWrite(2, HIGH);
  digitalWrite(3, LOW);
 }
 else if(col % 4 == 2) //COLUMN = 2, PIN 2
 {
  digitalWrite(0, HIGH); 
  digitalWrite(1, HIGH);
  digitalWrite(2, LOW);
  digitalWrite(3, HIGH);
 }
 else if(col % 4 == 3) //COLUMN = 3, PIN 1
 {
  digitalWrite(0, HIGH); 
  digitalWrite(1, LOW);
  digitalWrite(2, HIGH);
  digitalWrite(3, HIGH);
 }
 else if(col % 4 == 0) //  COLUMN 3, PIN 0
 {
  digitalWrite(0, LOW); 
  digitalWrite(1, HIGH);
  digitalWrite(2, HIGH);
  digitalWrite(3, HIGH);
 }
 col++;
} //END TOGGLECOL



void pinon(int pin)
{
  for(k = 5; k <= 13; k++)  //turning all rows off
  {
    digitalWrite(k, LOW);
  }
    digitalWrite(pin, HIGH); //activating correct row again
}//END PINON`

Answer 1

So I think at least one error is right here

void setup() {  //runs once
//  initialize pins as outputs
  for(int pinnum; pinnum >= lastpin; pinnum--) 
  {
    pinMode(pinnum, OUTPUT);
  }

above this you set pinnum = 13 But then in your for loop you say for(int pinnum...

This reinitializes pinnum to 0 so your for loop is not exicuting.

You can test this therory here http://www.compileonline.com/compile_cpp_online.php

Just copy and paste in the following and hit compile to see the difference

//Working for loop

#include <iostream>

using namespace std;

int main()
{
   cout << "Hello World" << endl; 
   int a = 10;

   for(a; a>0; a--){
      cout << a << endl;       
   }
   return 0;
}

Then try

//For loop like yours
#include <iostream>

using namespace std;

int main()
{
   cout << "Hello World" << endl; 
   int a = 10;

   for(int a; a>0; a--){
      cout << a << endl;           
   }
   return 0;
}