代码：

//矩阵计算器
#include <stdio.h>
void getmatrix(int m, int n, double m1[][n], double m2[][m]);
void calculate(int m, int n, double m1[][n], double m2[][m], double ansm[][m]);
void display(int m, int n, double m1[][n], double m2[][m], double ansm[][m]);
int main(void)
{
    int m, n;
    printf("Enter the size of the matrix:\n");
    printf("The number of rows:");
    scanf("%d", &m);
    printf("The number of columns:");
    scanf("%d", &n);
    const int m1[m][n];
    const int m2[n][m];
    int ansm[m][m];
    getmatrix(m, n, m1, m2);
    calculate(m, n, m1, m2, ansm);
    display(m, n, m1, m2, ansm);
    
    return 0;
}
void getmatrix(int m, int n, double m1[][n], double m2[][m])
{
    for (int i = 0; i < m; i++)
    {
        for (int j = 0; j < n; j++)
        {
            printf("Enter one number to complete matrix1:");
            scanf("%lf", &m1[i][j]);
        }
    }
    
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            printf("Enter one number to complete matrix2:");
            scanf("%lf", &m2[i][j]);
        }
    }
}

void calculate(int m, int n, double m1[][n], double m2[][m], double ansm[][m])
{
    int sum = 0;
    for (int i = 0; i < m; i++)
    {
        for (int j = 0; j < m; j++)
        {
            for (int k = 0; k < n; k++)
            {
                sum += m1[i][k] * m2[k][j];
            }
            ansm[i][j] = sum;
            sum = 0;
        }
    }
}

void display(int m, int n, double m1[][n], double m2[][m], double ansm[][m])
{
    printf("\nmatrix1:\n");
    for (int i = 0; i < m; i++)
    {
        for (int j = 0; j < n; j++)
        {
            printf("%6.1f", m1[i][j]);
        }
        printf("\n");
    }

    printf("\nmatrix2:\n");
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            printf("%6.1f", m2[i][j]);
        }
        printf("\n");
    }

    printf("\nThe answer of calculation:\n");
    for (int i = 0; i < m; i++)
    {
        for (int j = 0; j < m; j++)
        {
            printf("%6.1f", ansm[i][j]);
        }
        printf("\n");
    }
}

核心：

两个矩阵计算的算法：

int sum = 0;
    for (int i = 0; i < m; i++)
    {
        for (int j = 0; j < m; j++)
        {
            for (int k = 0; k < n; k++)
            {
                sum += m1[i][k] * m2[k][j];
            }
            ansm[i][j] = sum;
            sum = 0;
        }
    }