Predict the output of following C Program.
Output: The program compiles fine and produces following output:
Original Matrix
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
Matrix after modification
1 2 3 4
5 6 7 8
9 100 11 12
13 200 15 16
At first look, the line
"mat++;" in
modifyMatrix() seems invalid. But this is a valid C line as array parameters are always pointers (see
this and
this for details). In
modifyMatrix(),
mat is just a pointer that points to block of size
C*sizeof(int). So following function prototype is same as
"void modifyMatrix(int mat[][C])"
When we do mat++, mat starts pointing to next row, and mat[1][1] starts referring to value 10. mat[1][1] (value 10) is changed to 100 by the statement "mat[1][1] = 100;". mat is again incremented and mat[1][1] (now value 14) is changed to 200 by next couple of statements in modifyMatrix().
The line "mat[1][1] = 100;" is valid as pointer arithmetic and array indexing are equivalent in C.
On a side note, we can't do mat++ in main() as mat is 2 D array in main(), not a pointer.
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