Program to print and display identity matrix in C - c

Question

i am having trouble writing a program that prints a matrix, and then I generate the identity matrix. Here is my ccode below and any help would be greatly appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int PrintMatrix(int dim, double matrix[dim][dim]);
int main()
int PrintMatrix(int dim, double matrix[dim][dim]) {
int aa, bb;
for (aa = 0; aa <= dim; aa++) {
for (bb = 0; bb <= dim; bb++) {
printf("%lf ", matrix[aa][bb]);
}
printf("\n");
}
}
double TestMatrix[7][7] = {
{1,0,0,0,0,0,0},
{0,1,0,0,0,0,0},
{0,0,1,0,0,0,0},
{0,0,0,1,0,0,0},
{0,0,0,0,1,0,0},
{0,0,0,0,0,1,0},
{0,0,0,0,0,0,1}
};
PrintMatrix(7, TestMatrix);
return 0;

Answer 1

Your code won't compile successfully.
After main there is no opening brace.
You are defining function inside main, which is an issue.
Check for parentheses in whole code.
Fixed the loop controls from <= to <.
Here is the modified code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int PrintMatrix(int dim, double matrix[dim][dim]);
int main()
{
double TestMatrix[7][7] = {
{1,0,0,0,0,0,0},
{0,1,0,0,0,0,0},
{0,0,1,0,0,0,0},
{0,0,0,1,0,0,0},
{0,0,0,0,1,0,0},
{0,0,0,0,0,1,0},
{0,0,0,0,0,0,1},
};
PrintMatrix(7, TestMatrix);
return 0;
}
int PrintMatrix(int dim, double matrix[dim][dim]) {
int aa, bb;
for (aa = 0; aa < dim; aa++) {
for (bb = 0; bb < dim; bb++) {
printf("%lf ", matrix[aa][bb]);
}
printf("\n");
}
}

Answer 2

The code in the question is an appalling non-compiling mess. One of the comments is:
It still isn't returning the identity for dim = 2 up to 7; any thoughts?
As BluePixy hinted, if you lie to your compiler about the size of the input matrix to the function, for example by passing a 7x7 matrix but telling that it has a 3x3 matrix, it gets its revenge by printing different information from what you wanted. Don't lie to the compiler!
If you want to print identity matrices of sizes 1..7 from a 7x7 matrix, tell the compiler (function) both the actual size of the matrix and the size you want printed. For an identity matrix, you don't actually need the original matrix — you could synthesize the data.
#include <stdio.h>
static void printIdentityMatrix(int size)
{
for (int i = 0; i < size; i++)
{
for (int j = 0; j < size; j++)
printf("%4.1f", (i == j) ? 1.0 : 0.0);
putchar('\n');
}
}
int main(void)
{
for (int i = 1; i < 8; i++)
printIdentityMatrix(i);
return 0;
}
For printing the top left square subset of an arbitrarily sized square matrix, you must pass both the size of the data to be printed and the actual size of the matrix.
#include <assert.h>
#include <stdio.h>
static void PrintMatrix(int size, int dim, double matrix[dim][dim])
{
assert(size <= dim);
for (int aa = 0; aa < size; aa++)
{
for (int bb = 0; bb < size; bb++)
printf("%lf ", matrix[aa][bb]);
putchar('\n');
}
}
int main(void)
{
double TestMatrix[7][7] =
{
{1,0,0,0,0,0,0},
{0,1,0,0,0,0,0},
{0,0,1,0,0,0,0},
{0,0,0,1,0,0,0},
{0,0,0,0,1,0,0},
{0,0,0,0,0,1,0},
{0,0,0,0,0,0,1},
};
for (int i = 1; i < 8; i++)
{
PrintMatrix(i, 7, TestMatrix);
putchar('\n');
}
return 0;
}
Printing an arbitrary rectangular submatrix of an arbitrarily sized rectangular matrix requires many more function parameters (7 if I am counting correctly:
void PrintSubMatrix(int x_off, int y_off, int x_len, int y_len, int x_size, int y_size,
double matrix[x_size][y_size]);
and that's before you specify the file stream to write on.
#include <assert.h>
#include <stdio.h>
static void PrintSubMatrix(int x_off, int y_off, int x_len, int y_len, int x_size, int y_size,
double matrix[x_size][y_size])
{
assert(x_off >= 0 && x_off < x_size && x_off + x_len <= x_size);
assert(y_off >= 0 && y_off < y_size && y_off + y_len <= y_size);
printf("SubMatrix size %dx%d at (%d,%d) in M[%d][%d]\n",
x_len, y_len, x_off, y_off, x_size, y_size);
for (int x = x_off; x < x_off + x_len; x++)
{
for (int y = y_off; y < y_off + y_len; y++)
printf("%4.1f ", matrix[x][y]);
putchar('\n');
}
putchar('\n');
}
int main(void)
{
double TestMatrix[7][9] =
{
{ 1, 2, 3, 4, 3, 2, 1, 2, 3 },
{ 2, 1, 9, 8, 4, 6, 0, 0, 1 },
{ 3, 0, 8, 7, 5, 5, 0, 0, 1 },
{ 4, 0, 5, 6, 6, 8, 4, 4, 4 },
{ 5, 0, 1, 4, 7, 9, 0, 0, 1 },
{ 6, 0, 1, 0, 8, 1, 0, 0, 1 },
{ 7, 0, 0, 0, 9, 0, 1, 0, 1 },
};
PrintSubMatrix(0, 0, 7, 9, 7, 9, TestMatrix);
for (int i = 1; i < 4; i++)
{
for (int j = 2; j < 4; j++)
PrintSubMatrix(i, j, 3 + j - i, i + j, 7, 9, TestMatrix);
}
return 0;
}
Sample run:
SubMatrix size 7x9 at (0,0) in M[7][9]
1.0 2.0 3.0 4.0 3.0 2.0 1.0 2.0 3.0
2.0 1.0 9.0 8.0 4.0 6.0 0.0 0.0 1.0
3.0 0.0 8.0 7.0 5.0 5.0 0.0 0.0 1.0
4.0 0.0 5.0 6.0 6.0 8.0 4.0 4.0 4.0
5.0 0.0 1.0 4.0 7.0 9.0 0.0 0.0 1.0
6.0 0.0 1.0 0.0 8.0 1.0 0.0 0.0 1.0
7.0 0.0 0.0 0.0 9.0 0.0 1.0 0.0 1.0
SubMatrix size 4x3 at (1,2) in M[7][9]
9.0 8.0 4.0
8.0 7.0 5.0
5.0 6.0 6.0
1.0 4.0 7.0
SubMatrix size 5x4 at (1,3) in M[7][9]
8.0 4.0 6.0 0.0
7.0 5.0 5.0 0.0
6.0 6.0 8.0 4.0
4.0 7.0 9.0 0.0
0.0 8.0 1.0 0.0
SubMatrix size 3x4 at (2,2) in M[7][9]
8.0 7.0 5.0 5.0
5.0 6.0 6.0 8.0
1.0 4.0 7.0 9.0
SubMatrix size 4x5 at (2,3) in M[7][9]
7.0 5.0 5.0 0.0 0.0
6.0 6.0 8.0 4.0 4.0
4.0 7.0 9.0 0.0 0.0
0.0 8.0 1.0 0.0 0.0
SubMatrix size 2x5 at (3,2) in M[7][9]
5.0 6.0 6.0 8.0 4.0
1.0 4.0 7.0 9.0 0.0
SubMatrix size 3x6 at (3,3) in M[7][9]
6.0 6.0 8.0 4.0 4.0 4.0
4.0 7.0 9.0 0.0 0.0 1.0
0.0 8.0 1.0 0.0 0.0 1.0
It would be better if the code was fixed not to print a blank at the end of each line; that's left as an exercise for the reader.