Check the occurrence of a pattern in a string/text

	/**
	* Program to check the occurrences of a pattern in a text/string
	* This program checks whether the pattern occur in the string
	* or not, if yes at what positions and also print the text/string
	* highlighting the occurrences
	**/
	#include <stdio.h>
	#include<string.h>
	void check_substring(char *, char *);
	int main()
	{
	char str[500], substr[50];
	printf("\nEnter any string(Max length = 500 char):");
	fgets(str, 500, stdin);
	printf("\nEnter the pattern to be checked:");
	fgets(substr, 50, stdin);
	printf("\nstring = %s", str);
	printf("substring to be checked = %s", substr);
	check_substring(str, substr);
	return 0;
	}
	void check_substring(char *s, char *subs)
	{
	int i, j, k, no_of_occurence = 0;
	int l1, l2, f, pos;
	int position[100]; /* Keeps all positions where the
	substring occurs */
	l1 = strlen(s);
	printf("\n\nlength of string = %d", l1);
	l2 = strlen(subs);
	printf("\nlength of substring pattern being checked = %d", l2);
	k = 0;
	/* Traversing through the string */
	for(i = 0; i < l1; i++) {
	f = i;
	pos = i; /* Note the starting position */
	for(j = 0; j < l2; j++) {
	if(s[i] == subs[j])
	i++;
	else {
	i = f + 1;
	break;
	}
	}
	i--;
	/* On finding an occurrence */
	if(j >= l2) {
	/* Place start position in the position array */
	position[k++] = pos;
	no_of_occurence++;
	}
	}
	/* If the pattern occurs in the string/text */
	if(no_of_occurence > 0) {
	printf("\n\nThe substring occurs %d times at", no_of_occurence);
	/* Print all positions */
	for(i = 0; i < k; i++)
	printf("\nposition %d", position[i]);
	/* The string/text is printed with all occurrences enclosed
	between ^ and ^ */
	printf("\n\nThe text highlighting the occurrences of the substring\n ");
	k = 0;
	for(j = 0; j < l1; j++) {
	if(j == position[k])
	printf("^");
	printf("%c", s[j]);
	if(j == position[k] + l2 - 1) {
	printf("^");
	k++;
	}
	}
	}
	/* If the pattern does not occur in the string/text */
	else
	printf("\n\nThe substring does not occur in the string\n");
	}

view raw substring.c hosted with ❤ by GitHub

Written by Munia Balayil