C Program for Reversed String Pattern

In C programming, a reversed string pattern is a way to display a string in a triangular format where each row contains characters in reverse order, and when the string runs out, asterisks (*) fill the remaining positions. This creates an interesting visual pattern that grows row by row.

Syntax

void printReversedPattern(char str[], int length);

Algorithm

The approach to create this pattern involves the following steps −

• Start from the first row and print increasing number of characters
• For each row, calculate the starting position using formula: k = ((i*(i+1))/2)-1
• Print characters in reverse order, filling with '*' when string ends
• Move to the next line after completing each row

Example 1: Simple String Pattern

Let's create a reversed pattern for a simple string "abcd" −

#include <stdio.h>
#include <string.h>

void printReversedPattern(char str[], int n) {
    int i, j, k;
    
    for(i = 1; i <= n; i++) {
        k = ((i * (i - 1)) / 2) + i - 1;
        
        for(j = 0; j < i; j++) {
            if(k >= n) {
                printf("* ");
            } else {
                printf("%c ", str[k]);
            }
            k--;
        }
        printf("<br>");
    }
}

int main() {
    char str[] = "abcd";
    int length = strlen(str);
    
    printf("Input: %s<br>", str);
    printf("Pattern:<br>");
    printReversedPattern(str, length);
    
    return 0;
}

Input: abcd
Pattern:
a 
c b 
* * d 
* * * *

Example 2: Longer String Pattern

Here's an example with a longer string to better demonstrate the pattern −

#include <stdio.h>
#include <string.h>

void printReversedPattern(char str[], int n) {
    int i, j, k;
    
    for(i = 1; i <= n; i++) {
        k = ((i * (i - 1)) / 2) + i - 1;
        
        for(j = 0; j < i; j++) {
            if(k >= n) {
                printf("* ");
            } else {
                printf("%c ", str[k]);
            }
            k--;
        }
        printf("<br>");
    }
}

int main() {
    char str[] = "hello";
    int length = strlen(str);
    
    printf("String: %s<br>", str);
    printf("Reversed Pattern:<br>");
    printReversedPattern(str, length);
    
    return 0;
}

String: hello
Reversed Pattern:
h 
e l 
l l e 
o * * h 
* * * * *

How It Works

The pattern works by calculating the position of each character using the triangular number formula. For each row i, we start from position k = ((i*(i-1))/2) + i - 1 and move backwards, printing characters or asterisks as needed.

Key Points

• Each row contains one more character than the previous row
• Characters are printed in reverse order within each row
• When string characters are exhausted, asterisks (*) fill remaining positions
• The pattern continues until all rows are complete

Conclusion

The reversed string pattern is an interesting way to display strings in a triangular format. By using mathematical formulas and loops, we can create visually appealing patterns that demonstrate string manipulation techniques in C programming.