Print a Triangle of Stars Using Recursion

Say you want to print the following pattern based on the number of lines inputted:

Number of lines: 5
*****
****
***
**
*

You can do this using recursion (again, you could just do this iteratively, but whatever).

Code

#include <stdio.h>

void printRow(int n) {
	// doing this part iteratively because I refuse to do it recursively
	for (int i = 0; i < n; ++i) {
		printf("*");
	}
	printf("\n");
}

void printTriangle(int row) {
	if (row == 1) {
		// base step
		printf("*\n");
	} else {
		// recursive step
		printRow(row);
		printTriangle(row - 1);
	}
}

int main(void) {
	int lines = 5;
	printf("Number of lines: %d\n", lines);
	printTriangle(lines);
	return 0;
}

Print an Inverted Triangle of Stars Using Recursion

Say you want to print the following pattern based on the number of lines inputted:

Number of lines: 5
*
**
***
****
*****

You can do this using recursion (again, you could just do this iteratively, but whatever).

Code

#include <stdio.h>

void printRow(int row, int lines) {
// doing this part iteratively because I refuse to do it recursively
	for (int col = row - 1; col < lines; ++col) {
		printf("*");
	}
	printf("\n");
}

void printTriangle(int row, int lines) {
	if (row == 1) {
		// base step
		printRow(row, lines);
	} else {
		// recursive step
		printRow(row, lines);
		printTriangle(row - 1, lines);
	}
}

int main(void) {
	int lines = 5;
	printf("Number of lines: %d\n", lines);
	printTriangle(lines, lines);
	return 0;
}

Print a Pattern Recursively

Say you want to print the following pattern based on the number of lines inputted:

Enter number of max stars in a row: 5
*****
****
***
**
*
*
**
***
****
*****

Code

#include <stdio.h>

void printRow(int n);
void printPattern(int n);

int main(void) {
  int rows;
  printf("Enter number of max stars in a row:\n");
  scanf("%d", &rows);
  int rowsOverwrite = 5;
  printPattern(rowsOverwrite);
  return 0;
}

void printPattern(int n) {
  if (n > 0) {
    printRow(n);
    printPattern(n - 1); // recursive step
    printRow(n);
  }
}

void printRow(int n) {
  if (n == 1) {
	// base step
    printf("*\n");
  } else {
	// recursive step
    printf("*");
    printRow(n - 1);
  }
}

The reason this works is because printPattern(n-1) always runs before the second printRow, but after the first printRow. Thus, the recursive step is always squished between the printRow calls, which mirrors the output.

Also note that there is straight up no base step in the printPattern function; instead, the function just stops running.