Write a function that outputs a sideways triangle of height 2n-1 and width n, so the output for n = 4 would be:

*
**
***
****
***
**
*

One possible solution:

#include<stdio.h>
// This is the fastest way
int main(void) {
  int n;
  scanf("%d",&n);
  for(int i=0;i<n;i++) {
    for(int j=0;j<=i;j++)
      putchar(42);
    putchar(10);
  }
  for(int i=n-1;i>0;i--) {
    for(int j=0;j<i;j++)
      putchar(42);
    putchar(10);
  }
  while((n=getchar())!=10);
  getchar();
  return 0;
}

or like this (all math)

void sideways(int n)
{
    int i=0,j=0;
    for(i=1;i<2*n;i++){
        for(j=1;j<=(n-(abs(n-i)));j++){
	    printf("*");
	}
	printf("\n");
    }
}