C programming: A pyramid with asterisks - c

Question

What am I doing right? I am trying to learn a function.
This should be like this output:
*
***
*****
*******
My code:
#include <stdio.h>
#include <stdlib.h>
void pyramid (int n)
{
int width = 0;
if ( n )
{
++width;
pyramid( f, n - 1 );
for ( unsigned int i = 0; i < 2 * n - 1; i++ )
{
fprintf( f, "%*c", i == 0 ? width : 1, '*' );
}
fputc( '\n', f );
--width;
}
}
int main (int argc, char *argv[])
{
if (argc < 2)
{
printf ("usage: h4 <number>\n");
return 1;
}
pyramid (atoi (argv[1]));
return 0;
}
OUTPUT:
Python 3.6.1 (default, Dec 2015, 13:05:11)
[GCC 4.8.2] on linux
Traceback (most recent call last):
File "python", line 4
void pyramid (int n) {
^
SyntaxError: invalid syntax
Why is this problem? Please help me and explain. Thank you. I'm deaf C programmer beginner.

Answer 1

Another way to approach outputting the pyramid (centered) would be to use the field width modifier for your printf format string for the padding rather than the fill character itself. Then you can simply loop outputting the number of characters needed per line (which increases by 2 each line, e.g. 1, 3, 5, ...).
For example, taking the number of lines of output as the first argument to your program, (or using 4 by default if no argument is given), you could do something similar to the following:
#include <stdio.h>
#include <stdlib.h>
#define FILL '*'
void pyramid (int n)
{
if (n < 1) /* validate positive value */
return;
int l = 1, /* initial length of fill chars */
max = n * 2 - 1, /* max number of fill chars */
pad = max / 2; /* initial padding to center */
for (int i = 0; i < n; i++) { /* loop for each line */
if (pad) /* if pad remains */
printf ("%*s", pad--, " "); /* output pad spaces */
for (int j = 0; j < l; j++) /* output fill chars */
putchar (FILL);
putchar ('\n'); /* output newline */
l += 2; /* increment fill by 2 */
}
}
int main (int argc, char **argv) {
int n = argc > 1 ? (int)strtol (argv[1], NULL, 0) : 4;
pyramid (n);
return 0;
}
(note: you can use unsigned types throughout to insure positive values, or you can simply validate you have positive values. You should also include errno.h and validate the strtol conversion, though it will return 0 if no digits are provided)
It also helps to #define your fill character at the top of the code, so you have a convenient place for change should you want another character. It prevents digging through your function to find the constant later on.
Example Use/Output
$ ./bin/pyramidtop 1
*
$ ./bin/pyramidtop 5
*
***
*****
*******
*********
$ ./bin/pyramidtop 10
*
***
*****
*******
*********
***********
*************
***************
*****************
*******************

Answer 2

Disregarding for a minute how you seem to be running it with python, you are recursively calling the funtion here:
pyramid( f, n - 1 );
However, you only have it defined with one parameter, not with two.
Also, f is undefined.

Answer 3

Your file is a C file, try to compile it with gcc, not executing it with python
And you have some f variable that is not declared used, you can correct this:
#include <stdio.h>
#include <stdlib.h>
void pyramid (FILE *f, int n) {
int width = 0;
if ( n )
{
++width;
pyramid(f, n - 1 );
for ( unsigned int i = 0; i < 2 * n - 1; i++ )
{
fprintf( f, "%*c", i == 0 ? width : 1, '*' );
}
fputc( '\n', f );
--width;
}
}
int main (int argc, char *argv[])
{
if (argc < 2)
{
printf ("usage: h4 <number>\n");
return 1;
}
pyramid (stdout, atoi (argv[1]));
return 0;
}
Will give
*
***
*****
Your code can be updated to add spaces before stars and simplified:
Use clear variable names (stars instead of n)
2. Do not use fprintf where a simple fputc is enough
One variable is used to count stars, use one other to count spaces.
Will this consideration, your code should look like:
#include <stdio.h>
#include <stdlib.h>
/* use clear variable names */
void pyramid (FILE *f, int stars, int spaces) {
if ( stars>0 )
{
pyramid(f, stars -2, spaces + 1 );
for ( unsigned int i = 0; i < spaces; i++ )
{
/* use fputc when enough */
fputc(' ', f );
}
for ( unsigned int i = 0; i < stars; i++ )
{
fputc('*', f );
}
fputc( '\n', f );
}
}
int main (int argc, char *argv[])
{
if (argc < 2)
{
printf ("usage: h4 <number>\n");
return 1;
}
pyramid (stdout, atoi (argv[1]), 0);
return 0;
}
It gives:
*
***
*****

Answer 4

I wrote a much shorter, simpler version, using the formatting features of printf
#include <stdio.h>
int main(void) {
int height = 15;
char s[2*height-1];
memset(s,'*',2*height-1);
for(int i = 0; i<height; ++i)
{
printf("%*.*s\n", height+i,2*i+1,s);
}
return 0;
}
Output
Success #stdin #stdout 0s 9424KB
*
***
*****
*******
*********
***********
*************
***************
*****************
*******************
*********************
***********************
*************************
***************************
*****************************