String Pattern Matching Naive in DSA C - Build from Scratch

String Pattern Matching Naive

📖 Scenario: You are building a simple text search tool that looks for a small pattern inside a larger text. This is like finding a word in a book by checking each letter one by one.

🎯 Goal: Build a program that uses the naive method to find all positions where a given pattern appears in a text string.

📋 What You'll Learn

Create a character array text with the exact value "abracadabra"

Create a character array pattern with the exact value "abra"

Create an integer variable text_length that stores the length of text

Create an integer variable pattern_length that stores the length of pattern

Use a nested for loop with variables i and j to check for pattern matches in text

Print all starting indices where pattern is found in text separated by spaces

💡 Why This Matters

🌍 Real World

Searching for keywords in documents, logs, or DNA sequences using simple matching.

💼 Career

Understanding basic string search algorithms is essential for roles in software development, data processing, and bioinformatics.

1

Create the text and pattern strings

Create a character array called text with the exact value "abracadabra" and a character array called pattern with the exact value "abra".

DSA C

# Your code here

Hint

Use double quotes to create string arrays in C.

2

Calculate lengths of text and pattern

Create an integer variable called text_length that stores the length of text using sizeof(text) - 1. Create an integer variable called pattern_length that stores the length of pattern using sizeof(pattern) - 1.

DSA C

#include 

char text[] = "abracadabra";
char pattern[] = "abra";

// Your code here

Hint

Use sizeof to get the size of the array including the null character, so subtract 1.

3

Implement the naive pattern matching logic

Use a for loop with variable i from 0 to text_length - pattern_length. Inside it, use another for loop with variable j from 0 to pattern_length to check if pattern[j] matches text[i + j]. If all characters match, print the index i followed by a space.

DSA C

#include 

char text[] = "abracadabra";
char pattern[] = "abra";

int text_length = sizeof(text) - 1;
int pattern_length = sizeof(pattern) - 1;

// Your code here

Hint

Use nested loops to compare each character of the pattern with the text starting at index i.

4

Print a newline after all matches

Add a printf statement to print a newline character \n after printing all matching indices.

DSA C

#include 

char text[] = "abracadabra";
char pattern[] = "abra";

int text_length = sizeof(text) - 1;
int pattern_length = sizeof(pattern) - 1;

int i, j;
for (i = 0; i <= text_length - pattern_length; i++) {
    for (j = 0; j < pattern_length; j++) {
        if (text[i + j] != pattern[j]) {
            break;
        }
    }
    if (j == pattern_length) {
        printf("%d ", i);
    }
}

// Your code here

Hint

Use printf("\n") to move to the next line after printing all matches.