Ex quadro

#include <stdio.h>

#define TFL 20
#define TFC 20

void desenha(int x1, int y1, int x2, int y2);

int main(void)
{
    int x1, x2, y1, y2;

    scanf("%d %d", &x1, &y1);
    scanf("%d %d", &x2, &y2);

    desenha(x1, y1, x2, y2);
}

void desenha(int x1, int y1, int x2, int y2)
{
    int l, c, mat[TFL][TFC];

    for(l = 0; l < TFL; l++)
        for(c = 0; c < TFC; c++)
            mat[l][c] = 0;

    for(c = y1 - 1; c < y2; c++)
        mat[x1 - 1][c] = 1;

    for(l = x1; l < x2 - 1; l++)
    {
        mat[l][y1 - 1] = 1;
        mat[l][y2 - 1] = 1;
    }

    for(c = y1 - 1; c < y2; c++)
        mat[x2 - 1][c] = 1;

    for(l = x1 - 1; l < x2; l++)
    {
        for(c = y1 - 1; c < y2; c++)
        {
            if(mat[l][c] == 1)
                printf("|");
            else
                printf(" ");
        }

        printf("\n");
    }

    printf("\n\n\n");
}