コード:

#include <stdio.h>

void getShapeAndHeight(int *s, int *h)
{
    do {
        printf("形は？（1:○, 2:△, 3:□）"), scanf("%d", s);
    } while (!(1 <= *s && *s <= 3));
    do {
        printf("段数は？（1から20）"), scanf("%d", h);
    } while (!(1 <= *h && *h <= 20));
}

void drawPyramid(int n, int h)
{
    char *s[] = { "", "○", "△", "□" };
    int x, y;

    for (y = 0; y > -h; y--) {
        for (x = -h + 1; x <= h - 1; x++) {
            printf("%s", (y <= x && y <= -x) ? s[n] : "  ");
        }
        putchar('\n');
    }
}

int main(void)
{
    int shape, height;

    getShapeAndHeight(&shape, &height);
    drawPyramid(shape, height);
    return 0;
}

コード:

const char Circle[] = "○";
const char Triangle[] = "△";
const char Square[] = "□";
const char * const Shapes[3] = { Circle, Triangle, Square };  //配列

for( int i=0; i<3; ++i )
{	printf( "%s\n", Shapes[i] );	}  //配列添え字でどうの