Simple For loop not running!

[SeanDon44]

Below is my code for a project I am working on. The code gets past the first two groupings of For loops and then says Windows experienced and error and terminates the .exe file. From what I can tell this is nothing wrong, obviously to my beginner knowledge, with any references. Could someone please run it and see what their computer says. Or, tell me if I have an error in my code.
The output should be:
spot 1
spot 2
spot 3
spot 4
spot 4
spot 3
spot 2
spot 1
spot 5
spot 6
spot 7
spot 8
spot 12
spot 11
spot 10
spot 9
spot 13
spot 14
spot 15
spot 16

Code:
//Test of matrix manipulation
//12/24/15

#include <iostream>
using namespace std;

//This just gives each point a name for the sake of printing the pattern
char Point1[]="Spot 1";
char Point2[]="Spot 2";
char Point3[]="Spot 3";
char Point4[]="Spot 4";
char Point5[]="Spot 5";
char Point6[]="Spot 6";
char Point7[]="Spot 7";
char Point8[]="Spot 8";
char Point9[]="Spot 9";
char Point10[]="Spot 10";
char Point11[]="Spot 11";
char Point12[]="Spot 12";
char Point13[]="Spot 13";
char Point14[]="Spot 14";
char Point15[]="Spot 15";
char Point16[]="Spot 16";

//This is a dumby holder of the GPS Location to show the simple version of the grid system
char* array_2[4][4]={
//Col 0 1 2 3
{Point1,Point2,Point3,Point4},//Row 0
{Point5,Point6,Point7,Point8},//Row 1
{Point9,Point10,Point11,Point12},//Row 2
{Point13,Point14,Point15,Point16}//Row 3
};

//The matrix is only 4x4....Really the matrix/array will be dynamic from drive to drive....dependent on length and width of drive.
const int numRows=4;
const int numCols=4;
//This code provides the sweep pattern for the robot. Remember the std::out will be replaced with commands telling the robot what to do from point to point.
void pathcode(){
for(int row=0; row<1; ++row){
for(int col=0; col<numCols; ++col){
std::cout<<array_2[row][col]<<endl;} //Sweep first row right to left
}
for(int row=0; row<1; ++row){
for(int col=3; col<numCols; --col){
std::cout<<array_2[row][col]<<endl;} //sweep back to the first position of row 1
}
for(int row=1; row<2; ++row){
for(int col=0; col<=numCols; ++col){
std::cout<<array_2[row][col]<<endl;} //go to row 2 and sweep to the end
}
for(int row=2; row<3; ++row){
for(int col=3; col<=0; --col){
std::cout<<array_2[row][col]<<endl;} //drop a row and reverse sweep to row[0]
}
for(int row=3; row<=numRows-1; ++row){
for(int col=0; col<=numCols; ++col){
std::cout<<array_2[row][col]<<endl;} //drop to final row[3] and sweep last time right to left
}
}

//This simply runs the code. :)
int main(){
cout <<"Here is what your pattern will look like: "<< endl;
pathcode();
return 0;
}

[dhayden]

        for(int col=3; col<numCols; --col){
            std::cout<<array_2[row][col]<<endl;}

This lets col take on negative values, which produces an out-of-bounds access to array_2.

        for(int col=0; col<=numCols; ++col){
            std::cout<<array_2[row][col]<<endl;}

This allows col == 4, which results in out-of-bounds access

[Chervil]

There are several problems in the for loops.
I've left the original code preceded by a //

void pathcode()
{
    // Sweep first row right to left
    for (int row=0; row<1; ++row)
    {
        for (int col=0; col<numCols; ++col)
        {
            std::cout << array_2[row][col] << endl;
        } 
    }
    
    // sweep back to the first position of row 1
    for (int row=0; row<1; ++row)
    {
//      for (int col=3; col<numCols; --col)
        for (int col=numCols-1; col>=0; --col)
        {
            std::cout << array_2[row][col] << endl;
        } 
    }
    
    // go to row 2 and sweep to the end
    for (int row=1; row<2; ++row)
    {
//      for (int col=0; col<=numCols; ++col)
        for (int col=0; col<numCols; ++col)
        {
            std::cout << array_2[row][col] << endl;
        } 
    }
    
    //drop a row and reverse sweep to row[0]
    for (int row=2; row<3; ++row)
    {
//      for (int col=3; col<=0; --col)
        for (int col=numCols-1; col>=0; --col)
        {
            std::cout <<array_2[row][col] << endl;
        } 
    }
      
    // drop to final row[3] and sweep last time right to left
    for (int row=3; row<=numRows-1; ++row)
    {
//      for (int col=0; col<=numCols; ++col)
        for (int col=0; col<numCols; ++col)
        {
            std::cout << array_2[row][col] << endl;
        } 
    }
}

Hope that helps.

However the code is confusing to read as it gives the impression of a nested loop when the value of row does not change, thus there is no need for a loop.

void pathcode()
{
    // Sweep first row right to left
    for (int col=0, row=0; col<numCols; ++col)
        std::cout << array_2[row][col] << endl;

    // sweep back to the first position of row 1
    for (int col=numCols-1, row=0; col>=0; --col)
        std::cout << array_2[row][col] << endl;
         
    // go to row 2 and sweep to the end
    for (int col=0, row=1; col<numCols; ++col)
        std::cout << array_2[row][col] << endl;
    
    //drop a row and reverse sweep to row[0]
    for (int col=numCols-1, row=2; col>=0; --col)
        std::cout <<array_2[row][col] << endl;
    
    // drop to final row[3] and sweep last time right to left
    for (int col=0, row=3; col<numCols; ++col)
        std::cout << array_2[row][col] << endl;
}

[SeanDon44]

Thank you guys so much! I know this seems very basic stuff, obviously it is, but I am just learning c++. I am a mechanical engineer and just started getting into the world of coding! Chervil, The suggestion of the new for loops is very helpful! I didn't know that the for loop could take arguments like that. I understand the logic of coding basics but need to learn more of the syntax! Happy holidays!

[Chervil]

Glad that helped. The for loop is quite flexible. It combines several pieces of functionality into a single statement.

For example this code:

    for (int col=0, row=3; col<numCols; ++col)
        std::cout << array_2[row][col] << endl;

could be re-written like this:

{
    int col=0;
    int row=3;

    while  (col<numCols)
    {
        std::cout << array_2[row][col] << endl;
        
        ++col;
    }
}

Sometimes it may help to think of it that way, in order to visualise how it will behave.
See the tutorial page on control structures:
http://www.cplusplus.com/doc/tutorial/control/

[SeanDon44]

Very helpful again! I am going through the tutorial now and try sample examples!