Plotting a horizontal line

[hessajee]

I'm trying to create a horizontal line using a predefined colour between any two points on an image, which is 256 wide by 128 high, which is printed to a .ppm file that is then viewed using XnView. This is created by using a for loop which also contains code to create a vertical line, which works fine. I have been advised to use only one for loop on one of the variables, and then insert the other into the for loop. However, it is only printing out vertical lines and will print only one pixel for the horizontal line. Could anyone offer any tips on how to progress? The code is included below.

#include <stdio.h>
#include <math.h>
#define I_WIDE 256 // Define row with a value of 256 
#define I_HIGH 128 // Define column with a value of 128
#define RANGE 255 // Defines the range that the colour can take

void main (void)
{
    unsigned char image [I_WIDE] [I_HIGH] [3]; // Array of Predefined Values as shown above
    // Declare variables before the code, Intialise variables to 0
    int x = 0, y = 0;
    int xpos = 0, ypos = 5, end_xpos = 5, end_ypos = 5;
    int r1 = 55, g1 = 210, b1 = 38;
    FILE*ppmfile = NULL;
	
    for (y = ypos;y <= end_ypos; y++)
    {
          x = xpos; xpos < end_xpos; xpos++;
          image[x][y][0] = (unsigned char)r1; 
          image[x][y][1] = (unsigned char)g1; 
          image[x][y][2] = (unsigned char)b1;
    }
                          
    ppmfile = fopen("test.ppm","w"); // Opens the file to be written
    fprintf(ppmfile, "P3\n"); // Magic Number at the top of the document
    fprintf(ppmfile, "#test.ppm\n"); // Name of the document (Commented out)
    fprintf(ppmfile, "%d %d\n", I_WIDE, I_HIGH); // Inserts the size of the image into the document
    fprintf(ppmfile, "%d\n", RANGE); // number of colour variations in the document 
    
    
    for (y = 0; y < I_HIGH; y++)
    {
            for (x = 0; x < I_WIDE; x++)
            {
                    fprintf(ppmfile, "%4u %4u %4u \n", image[x][y][0], image[x][y][1], image[x][y][2]); // prints all of the different values
            }
    }

fclose(ppmfile); 
}

Thanks in advance.

[Salem]

> x = xpos; xpos < end_xpos; xpos++;
Is this meant to be a for loop?

[hessajee]

It was a for loop, but as I was told that one for loop would do the job, I removed it, hence producing the result mentioned earlier. Thank you for your question.

[Adak]

Why are you trying to make a horizontal line, using a y variable in a loop? You need an x variable in a loop, and no y.

[hessajee]

The reason being is that the same for loop will be able to print both vertical and horizontal lines. It should be able to go along the y, plotting the x values as appropriate, and vice versa depending on what is in the for loop. Hope that clarifies the matter.