Converting 2D array into a greyscale image in C - c

Question

I imported the 2d array of Lena using a header file (LenaArray.h); int lena [511][511] = {162,162,162,etc...},
but now I want to convert it into a greyscale image and I don't know how please help? Image of Lena I'm trying to print
#include <stdio.h>
#include "LenaArray.h"
int main () {
int i,j;
int width = 511;
int height = 511;
for (i = 0; i < height; i ++ )
{
for(j = 0; j < width; j ++)
{
printf("%d",&lena[i][j]);
}
}
}

Answer 1

#include <stdio.h>
typedef unsigned char U8;
typedef struct { U8 p[4]; } color;
U8 lena[511][511];
void save(char* file_name,int width,int height)
{
FILE* f = fopen(file_name, "wb");
color tablo_color[256];
for (int i = 0; i < 256; i++)
tablo_color[i] = { (U8)i,(U8)i,(U8)i,(U8)255 };//BGRA 32 bit
U8 pp[54] = { 'B', 'M', 0, 0, 0, 0, 0, 0, 0, 0, 54, 0, 0, 0 ,
40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 32 };
*(int*)(pp + 2) = 54 + 4 * width * height; //file size
*(int*)(pp + 18) = width;
*(int*)(pp + 22) = height;
*(int*)(pp + 42) = height * width * 4; //bitmap size
fwrite(pp, 1, 54, f);
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
U8 indis = lena[i][j];
fwrite(tablo_color+indis,4,1,f);
}
}
fclose(f);
}
int main()
{
for (int i = 0; i < 511; i++)
{
for (int j = 0; j < 511; j++)
{
lena[i][j]=i+j;
}
}
save("test.bmp", 511, 511);
}