{"id":6449,"date":"2024-06-22T00:01:10","date_gmt":"2024-06-22T07:01:10","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=6449"},"modified":"2024-06-14T21:48:37","modified_gmt":"2024-06-15T04:48:37","slug":"a-grid-of-random-stars-part-vi","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=6449","title":{"rendered":"A Grid of Random Stars, Part VI"},"content":{"rendered":"

The program may output what I want, but the code isn’t done yet. Continuing from last week’s Lesson<\/a>, I’d like the program to output a single grid showing a summary of all the rectangles found. This update requires more changes to the existing code.
\n
\nMy first attempt to create a single grid output resulted in a surprising reduction in the number of rectangles found. I don’t have a screenshot of the result, but the program went from finding 50+ rectangles to just a handful.<\/p>\n

After much gnashing of teeth, I discover that mapping out rectangles as each one was found resulted in many asterisks being overwritten. Therefore, fewer asterisks remained in the grid. Not good.<\/p>\n

To resolve this issue, I add a new array to the code: all[]<\/code>. It’s a rect<\/em> structure array, which stores the coordinates for each found rectangle. This data is gathered in the code’s main nested loop. When complete, the all[]<\/code> array is used to plot the rectangles. At that point, it doesn’t matter if any asterisks are overwritten as their location is already recorded.<\/p>\n

I also modified the update_grid()<\/em> function to avoid overwriting as much of the grid as possible. I don’t know if this change affected the output as it’s going to be a mess anyway.<\/p>\n

Here is the updated code:<\/p>\n

2024_06_22-Lesson.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <time.h>\r\n\r\n#define ROWS 16\r\n#define COLS ROWS*2\r\n#define SIZE COLS*ROWS\r\n#define PROB 5\r\n\r\nstruct rect {\r\n    int top;\r\n    int bottom;\r\n    int left;\r\n    int right;\r\n};\r\n\r\nvoid update_grid(char *g,struct rect r)\r\n{\r\n    int row,col;\r\n\r\n    for( row=0; row<ROWS; row++ )\r\n    {\r\n        for( col=0; col<COLS; col++ )\r\n        {\r\n            if(\r\n                    (row==r.top && (col>r.left && col<r.right) ) ||\r\n                    (row==r.bottom && (col>r.left && col<r.right) )\r\n              )\r\n                if( *(g+row*COLS+col) == '.' )\r\n                    *(g+row*COLS+col) = '-';\r\n            if(\r\n                    (col==r.left && (row>r.top && row<r.bottom) ) ||\r\n                    (col==r.right && (row>r.top && row<r.bottom) )\r\n                   )\r\n                if( *(g+row*COLS+col) == '.' )\r\n                    *(g+row*COLS+col) = '|';\r\n        }\r\n    }\r\n}\r\n\r\nint main()\r\n{\r\n    char *grid;\r\n    int row,col,count,x;\r\n    struct rect r,all[SIZE];\r\n\r\n    \/* seed the randomizer *\/<\/span>\r\n    srand( (unsigned)time(NULL) );\r\n\r\n    \/* allocate grid *\/<\/span>\r\n    grid = malloc( sizeof(char) * SIZE );\r\n    if( grid==NULL )\r\n    {\r\n        fprintf(stderr,\"Unable to allocate memory\\n\");\r\n        exit(1);\r\n    }\r\n\r\n    \/* fill and show the grid *\/<\/span>\r\n    puts(\"Original grid:\");\r\n    for( row=0; row<ROWS; row++ )\r\n    {\r\n        for( col=0; col<COLS; col++ )\r\n        {\r\n            if( rand() % PROB )\r\n                putchar( *(grid+row*COLS+col) = '.');\r\n            else\r\n                putchar( *(grid+row*COLS+col) = '*');\r\n        }\r\n        putchar('\\n');\r\n    }\r\n\r\n    count = 0;\r\n    \/* scan for two in a column *\/<\/span>\r\n    for( r.top=0; r.top<ROWS-1; r.top++ )\r\n    {\r\n        for( r.left=0; r.left<COLS; r.left++ )\r\n        {\r\n            \/* find a star in the row *\/<\/span>\r\n            if( *(grid+r.top*COLS+r.left) == '*' )\r\n            {\r\n                \/* look for a matching star in the same column *\/<\/span>\r\n                for( r.bottom=r.top+1; r.bottom<ROWS; r.bottom++ )\r\n                {\r\n                    if( *(grid+r.bottom*COLS+r.left) == '*' )\r\n                    {\r\n                        for( r.right=r.left+1; r.right<COLS; r.right++ )\r\n                        {\r\n                            if( *(grid+r.top*COLS+r.right)=='*' && *(grid+r.bottom*COLS+r.right)=='*' )\r\n                            {\r\n                                \/* add the grid to the array *\/<\/span>\r\n                                all[count] = r;\r\n                                count++;\r\n                            }\r\n                        }\r\n                    }\r\n                }\r\n            }\r\n        }\r\n    }\r\n\r\n    \/* build the full grid *\/<\/span>\r\n    for( x=0; x<count; x++ )\r\n        update_grid(grid,all[x]);\r\n\r\n    \/* output the final grid *\/<\/span>\r\n    printf(\"Found %d rectangles\\n\",count);\r\n    for( row=0; row<ROWS; row++ )\r\n    {\r\n        for( col=0; col<COLS; col++ )\r\n            putchar( *(grid+row*COLS+col) );\r\n        putchar('\\n');\r\n    }\r\n\r\n    return 0;\r\n}<\/pre>\n
In the main()<\/em> function, the original, pristine grid is output first. Then, in the nested loop, the call to update_grid()<\/em> is replaced with:all[count] = r;<\/code> The coordinates the struct rect<\/code> variable r<\/code> are saved to the all[]<\/code> array.<\/p>\n
After the main nested loop finishes, a for<\/em> loop calls update_grid()<\/em> to plot each of the rectangles found:<\/p>\n
for( x=0; x<count; x++ )
\n    update_grid(grid,all[x]);<\/code><\/p>\n
Finally, the updated grid is output, along with the count:<\/p>\n
Original grid:
\n*..........*.*.*...*.**..*......
\n.......*..........*........**.*.
\n....*......*............*..***.*
\n.*.......***...**..**.....*.....
\n..**.**..*......***.*......*....
\n*.....*.....*....*..*......*....
\n................**.*..*.*.......
\n......*.......*..*.*....**.**...
\n*..............*..**............
\n...*....*.....*.....**...*......
\n..........*..*.....*..*...**....
\n.....*.*..*......*...........*..
\n..*.*........*.................*
\n.........*...**......*..........
\n...*.......................**..*
\n..*...*......*....*.......**..*.
\nFound 71 rectangles
\n*----------*-*-*---*-**--*......
\n|......*...|.|.|..*|-||--|-**-*.
\n|...*------*-|-|--||-||-*|-***|*
\n|*..|....***---**--**||-||*||.||
\n|.**|**--*---|-|***|*||--|-*|.||
\n*.||||*---|-*|-||*||*||-|||*|.||
\n|.|||||...|..|.|**|*-|*-*||||.||
\n|.||||*---|--|*|-*|*-||-**-**.||
\n*--------------*--**|||..||||.||
\n..|*|-|-*-|--|*---||**|--*|||.||
\n..|||||...*--*-----*--*---**|.||
\n..|||*|*--*--|---*|..|....|||*||
\n..*|*--------*----|--|-----||-|*
\n..||..|..*...**------*....|||.||
\n..|*--|-----------|--------**-|*
\n..*---*------*----*-------**--*.<\/code><\/p>\n
This output could be made pretty by adding colors, which I may do in the future. But I did notice one more change that make the code easier to read: removing pointer notation. This update is presented in next week’s Lesson.<\/p>\n","protected":false},"excerpt":{"rendered":"
More fine tuning is required to get the code to where I want. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-6449","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6449","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6449"}],"version-history":[{"count":2,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6449\/revisions"}],"predecessor-version":[{"id":6453,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6449\/revisions\/6453"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6449"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6449"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6449"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}