C drawing patterns

 int patron(int n);

int n;

int main()
{
    printf("Introduce el numero natural deseado:\n");
    scanf("%d",&n);

    patron(n);
}

int patron(int n)
{
    int i, j;

    for(i=0; i<=n; i++)
    {
        for (j=1; j<=n; j++)
        {
            printf("+---");
        }
        printf("+\n");
        if(i<n){
           for (j=1; j<=n; j++)
            {
                printf("!   ");
            }
            printf("!\n");  
        }

    }
    printf("\n");
    return 0;
}

With this exercise, you will paint the drawing line by line. In this case, the odd lines will always be (+ ---) and the even lines will be (!). Control it with the counter of the first FOR, depending on whether it is even or odd you paint one thing or another.

I would do it this way, I would modify:

printf("+\n");

By

if(i != n)
    printf("+\n!   !   !   !\n");
else
    printf("+\n");

To make something like this:

In this example, n equals 3.

I leave you an alternative

void pintarCuadro(int n)
{

    for(int i=0; i<n+1; i++)
    {
   //    printf("pintar\n");
        for(int j=0; j<n; j++)
        {
            printf("+---");
        }
        printf("+\n");

        if(i<n)
        {
            for(int j=0; j<n; j++)
            {
                printf("!   ");
            }
            printf("!\n");

        }
    }
}

int main()
{

    pintarCuadro(7);


    return 0;
}

I show you an alternative way, which lets you choose the HIGH and the internal WIDTH of each cell.

Also, instead of doing multiple nested for , we precalculate the lines to be displayed, so instead of x * y iterations, we only do 3: precalculate the lines close , precalculate the internal lines, and a final loop to show them.

In the for final%, we check if we are on a line before the first line of crossover ; if we already pass it, we use the module (rest) of the division to know if we have to show an internal line of the cell, or a crossover .

As a last point, compile from C89 onwards.

#include <stdio.h>
#include <string.h>

#define ANCHO 2
#define ALTO 2

void showMatrix( int x ) {
  int realWidth = ( ANCHO * x ) + x + 1;
  char up[realWidth + 1];
  char inter[realWidth + 1];
  int idx;

  memset( up, '-', realWidth - 1 );
  up[realWidth] = 0;

  for( idx = 0; idx < realWidth; idx += ANCHO + 1 )
    up[idx] = '+';

  memset( inter, ' ', realWidth - 1 );
  inter[realWidth] = 0;

  inter[0] = '!';
  inter[realWidth - 1] = '!';
  for( idx = ANCHO + 1; idx < realWidth; idx += ANCHO + 1 )
    inter[idx] = '!';

  realWidth = ( ALTO * x ) + x + 1;

  printf( "%s\n", up );
  for( idx = 1; idx < realWidth ; ++idx )
    if( idx <  ALTO )
      printf( "%s\n", inter );
    else
      printf( "%s\n", idx % ( ALTO + 1 ) ? inter : up );
}

int main( void ) {
  showMatrix( 6 );

  return 0;
}

Thanks to everyone for the contributions, I have solved the problem, here is the final code:

    int patron(int n);
    int n;

    int main()
    {
        printf("Introduce el numero natural deseado:\n");
        scanf("%d",&n);

        patron(n);
    }

   int patron(int n)
   {
       int i, j,k, f;

       for(i=1; i<=n; i++)
       {
            for (j=1; j<=n; j++)
            {
                printf("+---");
            }
            printf("+\n");



            for (k=1; k<=n; k++)
            {
                printf("!   ");
            }

            printf("!\n");
            if (i==n){

                for (f=1; f<=n; f++)
                {
                    printf("+---");
                }
                printf("+\n");
            }


        }

        printf("\n");
        return 0;
   }

The addition was this zone (the rest of the code was not modified, it was simply added under the nested for):

     for (k=1; k<=n; k++)
        {
            printf("!   ");
        }

        printf("!\n");
        if (i==n){

            for (f=1; f<=n; f++)
            {
                printf("+---");
            }
            printf("+\n");
        }