Program 7 : String Matching

Develop a program to perform String Matching using Brute Force Method.

Brute Force String Matching

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

int bruteForceMatch(char text[], char pattern[]) {
    int n = strlen(text);
    int m = strlen(pattern);

    for (int i = 0; i <= n - m; i++) {
        int j;
        for (j = 0; j < m; j++) {
            if (text[i + j] != pattern[j])
                break;
        }
        if (j == m)
            return i;  
            // Match found at index i
    }
    return -1;  
    // No match found
}

int main() {
    char text[1000], pattern[100];

    printf("Enter the text: ");
    fgets(text, sizeof(text), stdin);
    text[strcspn(text, "\n")] = '\0';  // Remove newline

    printf("Enter the pattern: ");
    fgets(pattern, sizeof(pattern), stdin);
    pattern[strcspn(pattern, "\n")] = '\0';  // Remove newline

    int position = bruteForceMatch(text, pattern);

    if (position != -1)
        printf("Pattern found at position %d\n", position);
    else
        printf("Pattern not found in the text.\n");

    return 0;
}

• It loops over every possible starting position i in the text (from 0 to n - m).

• For each position, it checks if the substring of length m starting at i matches the pattern.

• If it matches, it returns the starting index i.

• If no match is found, it returns -1.

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Reading Input with fgets()

printf("Enter the text: ");
fgets(text, sizeof(text), stdin);
text[strcspn(text, "\n")] = '\0';  // Remove newline

• scanf("%s", text) stops at spaces — fgets is better for reading full sentences.

fgets(text, sizeof(text), stdin);

• Reads a full line of input (including spaces) from the user and stores it in the text array.

• sizeof(text) ensures you don’t read beyond the array size.

text[strcspn(text, "\n")] = '\0';

• fgets() includes the newline character (\n) when the user presses Enter.

• strcspn(text, "\n") finds the index of the newline.

• This line replaces \n with \0, effectively removing the newline from the input string.