Find the first occurrence of a substring in a string

Posted on Apr 21, 2020

C program to find the first occurrence of a substring in a given string.

Program

#include<stdio.h>
#include<conio.h>
#define MAX 50

void main()
{
	char str[MAX], sub_str[MAX];
    int i, j, flag;

    printf("Enter the string\t:");
    gets(str);
    printf("Enter substring to be searched\t:");
    gets(sub_str);

    i = 0;
    while(str[i] != '\0')
    {
        if(str[i] == sub_str[0])
        {
            j = 0;
            flag = 1;
            while(sub_str[j] != '\0')
            {
                if(str[i+j] != sub_str[j])
                {
                    flag = 0;
                    break;
                }
                j++;
            }
        }
        if(flag == 1)
        {
            break;
        }
        i++;
    }

    if(flag == 1)
    {
        printf("\nSubstring '%s' found at position %d",sub_str,i+1);
    }
    else
    {
        printf("\nSubstring not found");
    }

    getch();
}

Output

Enter the string        :welcome to coursecrux.com
Enter substring to be searched  :co

Substring 'co' found at position 4