Problem number 01 and 02

#include<stdio.h>
int main()
{
    int r,c,m,n,i,sum1=0,sum=0;
    printf("Dimension of your matrix [?]*[?] = \n");
    scanf("%d%d",&m,&n);
    printf("Enter your element :\n");
    int mat[m][n];
    for(r=0;r<m;r++)
    {
        for(c=0;c<n;c++)
            {
                scanf("%d",&mat[r][c]);
                sum1=sum1+mat[r][c];
            }
    }
    printf("\n");
    for(r=0;r<m;r++)
    {
        for(i=0;i<n;i++)
        {printf("------|");}
        printf("\n");
        for(c=0;c<n;c++)
            {
                if(mat[r][c]<=9)
                printf("   %d  |",mat[r][c]);
                else if(mat[r][c]>=10&&100>mat[r][c])
                printf("  %d  |",mat[r][c]);
                else if(mat[r][c]>=100&&1000>mat[r][c])
                printf("  %d |",mat[r][c]);
                else if(mat[r][c]>=1000&&10000>mat[r][c])
                printf(" %d |",mat[r][c]);
                else if(mat[r][c]>=10000&&100000>mat[r][c])
                printf(" %d|",mat[r][c]);
                else
                printf("%d|",mat[r][c]);
            }
        printf("\n");
    }
    for(i=0;i<n;i++)
        {printf("------|");}
    printf("\n");
    printf("\n");
    printf(" sum of all elements = %d\n",sum1);
    printf(" Diagonal element : ");
    for(r=0;r<m;r++)
        {
            for(c=0;c<n;c++)
            {
                if(r==c)
                {
                    printf("%d ",mat[r][c]);
                    sum=sum+mat[r][c];
                }
            }
        }
        printf("\n Sum of diagonal element = %d",sum);
        printf("\n");
    return 0;
}