Grids, or matrixes, are a common data thingy, as information often appears in tables. Being able to fold, spindle, and mutilate a grid is a common computer programming task, something to entertain your idle hours even if you have no pressing need to manipulate a matrix.
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\nBefore I abuse a matrix\/grid, it must be created. Two approaches are available: traditional array notation and pointer nightmare.<\/p>\n
Array notation is easier, so it comes first:<\/p>\n
\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <time.h>\r\n\r\n#define SIZE 3\r\n\r\nint main()\r\n{\r\n int x,y;\r\n int grid[SIZE][SIZE];\r\n\r\n \/* seed the randomizer *\/<\/span>\r\n srand( (unsigned)time(NULL) );\r\n\r\n \/* populate the grid *\/<\/span>\r\n for( x=0; x<SIZE; x++ )\r\n for( y=0; y<SIZE; y++ )\r\n grid[x][y] = rand()%10 + 1;\r\n\r\n \/* output the grid *\/<\/span>\r\n for( x=0; x<SIZE; x++ )\r\n {\r\n for( y=0; y<SIZE; y++ )\r\n printf(\" %d \",grid[x][y]);\r\n putchar('\\n');\r\n }\r\n\r\n return(0);\r\n}<\/pre>\nThe defined constant SIZE<\/code> sets the grid’s row and column count — a square. In this example, the matrix is 3×3 (or SIZE<\/code> x SIZE<\/code>) integers, which is how the grid[][]<\/code> two-dimensional array is declared at Line 10.<\/p>\nAfter seeding the randomizer, nested for<\/em> loops populate the grid: rows (variable x<\/code>) by columns (variable y<\/code>). Random values in the range of 1 through 10 populate the matrix: rand()%10 + 1<\/code><\/p>\nA second set of nested for<\/em> loops outputs the grid, setting a newline between each row.<\/p>\nHere’s a sample run:<\/p>\n
4 7 1
\n 2 3 7
\n 8 5 9<\/code><\/p>\nAs I’m fond of writing, a two-dimensional array is merely a one-dimensional array all gussied up for programmer readability. Honestly, it’s all one chunk of data in memory anyway. But the double bracket notation makes things easier to read — as long as you don’t forget that the first array element is zero, not one.<\/p>\n
To pervert the same code into a pointer version, I rely upon the assumption that the matrix is just one long chunk of data. The same SIZE<\/code> constant defines the dimensions and manipulates the data as a matrix. The code is a little tighter in some spots, but requires more statements as the matrix buffer must be allocated.<\/p>\n2023_02_25-Lesson-b.c<\/a><\/h3>\n\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <time.h>\r\n\r\n#define SIZE 3\r\n\r\nint main()\r\n{\r\n int x;\r\n int *grid;\r\n\r\n \/* seed the randomizer *\/<\/span>\r\n srand( (unsigned)time(NULL) );\r\n\r\n \/* allocate the grid *\/<\/span>\r\n grid = malloc( sizeof(int) * SIZE * 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 \/* populate the grid *\/<\/span>\r\n for( x=0; x<SIZE*SIZE; x++ )\r\n *(grid+x) = rand()%10 + 1;\r\n\r\n \/* output the grid *\/<\/span>\r\n for( x=0; x<SIZE*SIZE; x++ )\r\n {\r\n printf(\" %d \",*(grid+x));\r\n if( (x+1)%3 == 0 )\r\n putchar('\\n');\r\n }\r\n\r\n free(grid);\r\n return(0);\r\n}<\/pre>\nStorage is allocated at Line 16, assigned to int<\/em> pointer variable grid<\/code>:<\/p>\ngrid = malloc( sizeof(int) * SIZE * SIZE );<\/code><\/p>\nThe SIZE * SIZE<\/code> calculation allocates the same size as the two-dimensional array. Then a test is made to ensure storage was successfully allocated.<\/p>\nOnly a single for<\/em> loop is required to assign values to the matrix, again using SIZE*SIZE<\/code> to set the quantity of integers required. The expression *(grid+x)<\/code> ensures that the values are set at the proper offset.<\/p>\nA single for<\/em> loop is all that’s needed to output the matrix. An if<\/em> statement determines when SIZE<\/code> items are output — if( (x+1)%3 == 0 )<\/code> — at the end of a row, a newline is output. Here’s the sample run:<\/p>\n 1 8 5
\n 9 7 3
\n 5 3 1<\/code><\/p>\nYes, it’s the same output, just a different approach. Either way, the matrix is created and prepped for abuse.<\/p>\n
For next week’s Lesson<\/a>, the task is to total each of the rows and columns.<\/p>\n","protected":false},"excerpt":{"rendered":"The first step toward grid nirvana, is to construct and populate the grid. Continue reading