why the output is blank?

Question

I have to write a program for matrix multiplication.there may be an easier algorithm,but i want to know what is the problem here and if there is anything wrong with my algorithm or .... if there is any need for additional info,please tell me.the program should multiply two matrixes with variable sized columns and rows.I`m a begginner so my mistake could be realy obvious.

#include <stdio.h>

int main()
{
    int m,n,l,a,b;
    scanf("%d %d %d",&m,&n,&l);
    int A[m][n],B[n][l],AB[m][l];
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++) scanf("%d",&A[i][j]);
    }
     for(int i=0;i<n;i++){
        for(int j=0;j<l;j++) scanf("%d",&B[i][j]);
    }
      for(int i=0;i<m;i++){
        for(int j=0;j<l;j++) AB[i][j]=0;
    }
    
     for(int i=0;i<m;i++){
        for(int j=0;j<l;j++){
            a=n;
            b=0;
            while(a!=0){
                AB[i][j]=AB[i][j]+A[i][b]*B[b][j];
                a=a--;
                b=b++;
            }
        }
    }
   for(int i=0;i<m;i++){
        for(int j=0;j<l;j++){
            printf("%d ",AB[i][j]);
        }
        printf("\n");
   }
}

so I changer it according to the comments,did i do it right?because the new problem is that it is not running.I click enter but it just goes to the next line instead of showing the output.

Answer 1

Changed increment/decrement instructions and added output statements:

#include <stdio.h>

int main()
{
    int m,n,l,a,b;
    printf("Enter m, n, l: ");
    scanf("%d %d %d",&m,&n,&l);
    int A[m][n],B[n][l],AB[m][l];
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++) {
            printf("Enter A[%d][%d]: ", i, j);
            scanf("%d",&A[i][j]);
        }
    }
    for(int i=0;i<n;i++){
        for(int j=0;j<l;j++) {
            printf("Enter B[%d][%d]: ", i, j);
            scanf("%d",&B[i][j]);
        }
    }
    for(int i=0;i<m;i++){
        for(int j=0;j<l;j++) AB[i][j]=0;
    }
    
    for(int i=0;i<m;i++){
        for(int j=0;j<l;j++){
            a=n;
            b=0;
            while(a!=0){
                AB[i][j]=AB[i][j]+A[i][b]*B[b][j];
                a=a-1;
                b=b+1;
            }
        }
    }
    for(int i=0;i<m;i++){
            for(int j=0;j<l;j++){
                printf("%d ",AB[i][j]);
            }
            printf("\n");
    }
}

$ gcc -Wall matrix.c
$ ./a.out           
Enter m, n, l: 2 2 2
Enter A[0][0]: 1
Enter A[0][1]: 1
Enter A[1][0]: 1
Enter A[1][1]: 1
Enter B[0][0]: 2
Enter B[0][1]: 2
Enter B[1][0]: 2
Enter B[1][1]: 2
4 4 
4 4 
$

The output does not look blank to me. :-)