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POPointers in C, returning from functions?
 

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  1. POPointers in C, returning from functions?
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    <p>I am trying to create a simple matrix multiplication program in C. To do this I have opted to use 2 functions: 1 to simply create matrices, and 1 to hold all the created matrices (for doing multiplication).</p> <p>I have finally managed to work out how to pass an array from a function (or more specifically pass a pointer to the array from a function), however, I want the function matrixWelcome() below to be passed the number of rows &amp; columns of the array. This is where I am stuck.</p> <p>Currently gcc is giving me error invalid type argument of ‘unary *’ for line -> rows = *i;</p> <p>My code is:</p> <pre><code>void matrixWelcome() { int selection; int a, b, c, d, *rows, *columns; int *matrix1[0][0], *matrix2[0][0]; printf("Welcome to matrix mode\n"); printf("Please select from the following: \n"); printf("1 - Matrix multiplication"); scanf("%d", &amp;selection); switch (selection) { case 1: printf("Selected matrix multiplication...\n"); printf("Please enter matrix 1\n"); matrix1[*rows][*columns] = matrixInput(*rows, *columns); printf("%d\n", *matrix1[1][1]); a = *rows; b = *columns; printf("****ROWS = %d, COLUMNS = %d", a, b); // printf("Matrix 1 has %d rows and %d columns", rows, columns); printf("Please enter matrix 2\n"); // matrix2 = matrixInput(); break; default: printf("No input entered\n"); break; } } int *matrixInput(int *rows, int *columns) { int i, j, x, y; int *array_pointer = malloc(5 * sizeof(int)); //grab some memory if (array_pointer == NULL) { // check that we have successfully got memory return NULL; } // Number of rows &amp; columns for matrix 1 printf("Enter number of rows: "); scanf("%d", &amp;i); printf("\nEnter number of columns: "); scanf("%d", &amp;j); rows = *i; columns = *j; // Initialise 2D array to hold values int matrix_input[i][j]; printf("Enter values for matrix, starting at 1,1 and moving across 1st row; then move across 2nd row etc.."); // loop to store values in matrix for (x=0; x&lt;i; x++) { for (y=0; y&lt;j; y++) { int value_entered; scanf("%d", &amp;value_entered); matrix_input[x][y] = value_entered; } } *array_pointer = matrix_input[i][j]; // print out matrix - just to confirm printf("You've entered the following matrix: \n"); for (x=0; x&lt;i; x++) { for (y=0; y&lt;j; y++) { printf("%4d", matrix_input[x][y]); } printf("\n"); } return array_pointer; } </code></pre> <p>Any help would be appreciated.</p>
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    1. USBrendan Long
    1. UScud_programmer
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      1. VTUpMod
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    1. COw.r.t. the title: remember, a pointer to an object is only valid for that objects lifetime. (e.g. a pointer to an array declared in a function is invalid once the function returns.)
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