Question

A program to check if 2nd string is a substring of first string. It displays “Yes” for all cases, Moreover, I get a runtime error whenever i give the second string as ‘q**q’, why is it so..? * stand for any letter.

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
    char str1[20], str2[20];
    int l1, l2, i1, i2=0;
    gets(str1);
    gets(str2);
    l1=strlen(str1);
    l2=strlen(str2);
    if(l1>=l2)
    {
        for(i1=0; i1<=l1-l2+i2, i2<l2; i1++)
        {
            if(str2[i2]==str1[i1])
            i2++;
        }
        if(i2==l2)
            printf("Yes");
        else
            printf("No");
    }
    else
        printf("No");

    getch();

    return 0;
}

Answer 1

The condition in the for statement

for(i1=0; i1<=l1-l2+i2, i2<l2; i1++)

really doesn’t make sense. The code i1<=l1-l2+i2, i2<l2 evaluates the part before the comma, discards the result, and then evaluates the part after the comma.

Perhaps you intend to write i1<=l1-l2+i2 && i2<l2.