Allocate memory for 2D array dynamically

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Question:
Please implement it in C - To allocate memory for real 2D array dynamically, be reminded to insert your code based on the comments below accordingly.
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#include <stdlib.h>
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​
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int main(void){
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​
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    int **a, m = 500, n = 400, 1, j;
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    // Allocate memory for a[m][n] here
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    // Insert your code:
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​
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​
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​
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​
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​
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    for ( i = 0; i < m; i++){
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        for (j = 0; j < n; j++){
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            a[i][j] = i+j;
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        }
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    }
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    return 0;
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}
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Answer:
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#include <stdio.h>
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#include <stdlib.h>
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​
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​
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int main(void){
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​
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    int **a, m = 500, n = 400, i, j;
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    // Allocate memory for a[m][n] here
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    // Insert your code:
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​
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​
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    a = (int**) malloc(m * sizeof(int*));
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    for(int k = 0; k < m; k++){
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        a[k] = (int*) malloc (n * sizeof(int));
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​
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    }
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​
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​
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    for ( i = 0; i < m; i++){
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        for (j = 0; j < n; j++){
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            a[i][j] = i+j;
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        }
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    }
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​
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    for ( int k = 0; k < m; k++){
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        for (int r = 0; r < n; r++){
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            printf("a[%d][%d] = %d \n", k, r, a[k][r]);
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        }
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    }
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    for (int t = 0; t < m; t++)
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        free(a[t]);
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    free(a);
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    return 0;
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}
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​
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