#include <stdio.h>
#include <strings.h>

double A[3][2] = {{1,2}, {3,4}, {5,6}};
double X[2] = {7,8};
void matprint(int m,int n,double A[m][n]){
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
            printf("%g %lu ",A[i][j],
                (long unsigned)&A[i][j]);
        }
        printf("\n");
    }
}
void vecprint(int m,double X[m]){
    matprint(m,1,(double (*)[1])X);
}
void multAx(int m,int n,
    double A[m][n],double X[n],double B[m]){
    bzero(B,sizeof(double)*m);
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
            B[i]+=A[i][j]*X[j];
        }
    }
}
void algob(int m,int n,
    double A[m][n],double X[n],double B[m]){
    bzero(B,8*m);
    for(int j=0;j<n;j++){
        for(int i=0;i<m;i++){
            B[i]+=A[i][j]*X[j];
        }
    }
}
int main(){
    double B[3];
    printf("A=\n"); matprint(3,2,A);
    printf("X=\n"); vecprint(2,X);
    multAx(3,2,A,X,B);
    printf("B=\n"); vecprint(3,B);
    return 0;
}