C program — coding the figure given n when n is odd? - c

Question

I have to display the following figure (The two triangles intercept) for a n given by the user, where n is odd. The figure is in this link: http://i.imgur.com/mQxarLz.jpg
*******
*****
***
*
*
***
*****
*******
I already wrote this code, but I don't know how to give the n, where n is odd. And my code doesn't compile; it says: "In the fifth row, syntax error before for".
#include <stdio.h>
int main (void) {
int n,i,k,m;
for(m=0;m<2;m++)
for (i=1;i<=n;i++){
if(m==0){
for(k = 1; k<=n-i; k++){
printf(" ");
}
}
}
for (k=1;k<2*i;k++){
printf("%s","*");
//printf("%d",i);
}
scanf("%d",&n);
for (k = 1; k<=i;k++)
for (k=1;k<(n-i)*2;k++)
for (i=1;i<=n;i++) {
printf("\n$");
}
return 0;
}

Answer 1

First, the answer to "how do I check whether an integer is odd": you simply divide by 2 and check if the remainder is 0 (even) or 1 (odd). In C and most related languages, this is what the modulo operator "%" does:
if ((n % 2) == 1) {
// The number is odd.
}
But you should make sure that you read your n right at the start, because in the code that you have submitted, n is read in your second "for" loop before you have actually written something to it. And that means, n contains garbage at that point.

Answer 2

Good programming is to solve problems in the most simple way you can find. This particular algorithm is really fundamental stuff, thus you shouldn't end up with anything much more complicated than this:
#include <stdio.h>
#include <stdbool.h>
void print_chars (char symbol, int n)
{
for(int i=0; i<n; i++)
{
printf("%c", symbol);
}
}
void print_triangle (int base_size, int height, bool pointing_up)
{
int star_count = pointing_up ? 1 : base_size;
for(int row = 0; row < height; row++)
{
int spaces = base_size - star_count;
print_chars (' ', spaces/2);
print_chars ('*', star_count);
print_chars (' ', spaces/2);
printf("%\n");
star_count += pointing_up ? 2 : -2;
}
}
int main (void)
{
print_triangle(7, 4, false);
print_triangle(7, 4, true);
}
Note that the above code will behave strange if the triangle's base isn't in sync with its height - I left that out intentionally, feel free to improve the program further with such.

Answer 3

#include <stdio.h>
void printAsterisk(int n, int length){
int i, slen = (length - n)/2;
for(i=0;i < slen;++i)
putchar(' ');
for(i=0;i < n;++i)
putchar('*');
putchar('\n');
}
/* non-recursive
void printTriangle(int n, int length){//n isn't required as an argument
int d= -2;
for(; n < length + 1; n += d){
if(n < 0) n += (d *= -1);
printAsterisk(n, length);
}
}
*/
void printTriangle(int n, int length){
if(n < 1) return;
printAsterisk(n, length);
printTriangle(n - 2, length);
printAsterisk(n, length);
}
int main(void){
int n;
do{
printf("input odd number:");
scanf("%d", &n);
}while(n % 2 == 0);
printTriangle(n, n);
return 0;
}