Hollow Butterfly Dry Run in C

Hollow Butterfly is an interactive C dry run visualizer from the Patterns programs section. Study the source code, then use the execution controls to follow each step, variable update, highlighted line, and console output.

This page provides a browser-based dry run with source-code highlighting, auto-scroll, voice narration controls, and execution output for learning the program step by step.

Hollow Butterfly Program Code

#include <stdio.h>
int main() {
    int n = 4, i, j;
    // Upper
    for(i = 1; i <= n; i++) {
        for(j = 1; j <= i; j++) {
            if(j == 1 || j == i) printf("*");
            else printf(" ");
        }
        for(j = 1; j <= 2 * (n - i); j++) printf(" ");
        for(j = 1; j <= i; j++) {
            if(j == 1 || j == i) printf("*");
            else printf(" ");
        }
        printf("\n");
    }
    // Lower
    for(i = n; i >= 1; i--) {
        for(j = 1; j <= i; j++) {
            if(j == 1 || j == i) printf("*");
            else printf(" ");
        }
        for(j = 1; j <= 2 * (n - i); j++) printf(" ");
        for(j = 1; j <= i; j++) {
            if(j == 1 || j == i) printf("*");
            else printf(" ");
        }
        printf("\n");
    }
    return 0;
}

View the complete Patterns programs page.