Question

How do I write an array of y[7990272] values to a text file (opened using the fopen() function) in a 2448×3264 order (so each row in the text file has 2448 values).

FILE *fp;

fp=fopen("output.txt","w");

for(int i=0;i<7990272;i++)
{
    fprintf(fp,"%f\n",y[i]);
}
fclose(fp);

Answer 1

for (int i = 0; i < 3264; i++)
{
    for (int j = 0; j < 2448; j++)
        fprintf(fp, "%f", y[i*2448+j]);
    putc('\n', fp);
}

The residual issue is that there won’t be any spaces between the numbers as written. There are various ways to handle that; I usually use a variation on:

for (int i = 0; i < 3264; i++)
{
    const char *pad = "";
    for (int j = 0; j < 2448; j++)
    {
        fprintf(fp, "%s%f", pad, y[i*2448+j]);
        pad = " ";
    }
    putc('\n', fp);
}

If you don’t like the recomputation of the array subscript, you can keep another variable that simply increments monotonically:

index = 0;
for (int i = 0; i < 3264; i++)
{
    const char *pad = "";
    for (int j = 0; j < 2448; j++)
    {
        fprintf(fp, "%s%f", pad, y[index++]);
        pad = " ";
    }
    putc('\n', fp);
}