matrix multiplication

/*Please consider saving the code of 'array function'(from my pastebin) as 'functions.c' in the same folder as the following code is saved*/
#include<stdio.h>
#include"functions.c"

int main(){
    int order;
    int sum;
    printf("Only square matrices are allowed\nWhat is the order of matrices: ");
    scanf("%d", &order);

    int mat1[order][order];
    input_matrix(order, mat1);
    printf("Matrix 1 is:\n");
    display_matrix(order, mat1);

    int mat2[order][order];
    input_matrix(order, mat2);
    printf("Matrix 2 is:\n");
    display_matrix(order, mat2);

    int mat_result[order][order];
    for(int i=0; i<order; i++){
        for(int j=0; j<order; j++){
            sum=0;
            for(int k=0; k<order; k++){
                sum = sum+mat1[i][k]*mat2[k][j];
            }
            mat_result[i][j] = sum;
        }
    }
    printf("Multiplication is: \n");
    display_matrix(order, mat_result);
    return 0;
}