C - check if a string is a substring of another string

Question

I need to write a program that takes two lines as arguments and checks if the second is a substring of the first. I need to do this without using any special library functions. I created this implementation, but I think that it always returns true if there is one letter that is the same on both lines. You can help me here. I'm not sure what I'm doing wrong:

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

int my_strstr( char const *s, char const *sub ) {
    char const *ret = sub;

    int r = 0;
    while ( ret = strchr( ret, *sub ) ) {
        if ( strcmp( ++ret, sub+1 ) == 0 ){
            r = 1;
        }
        else{
            r = 0;
        }        
    }
    return r;
}

int main(int argc, char **argv){

    if (argc != 3) {
        printf ("Usage: check <string one> <string two>\n");
    }
    int result = my_strstr(argv[1], argv[2]);

    if(result == 1){
        printf("%s is a substring of %s\n", argv[2], argv[1]);
    } else{
        printf("%s is not a substring of %s\n", argv[2], argv[1]);
    }
    return 0;
}

Answer 1

Your approach to writing strstris fundamentally wrong. Let's see what you wrote:

char const *ret = sub;

int r = 0;
while ( ret = strchr( ret, *sub ) ) {
    if ( strcmp( ++ret, sub+1 ) == 0 ){
        r = 1;
    }
    else{
        r = 0;
    }        
}
return r;

, ret, sub, sub s. , ret s...

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Answer 2

, ret my_strstr. strcmp , . , strncmp.

Answer 3

, char * sub char * sub:

int my_strstr( char const *s, char const *sub ) {
char const *ret = sub;

ret s?

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Answer 4

ret = strchr( ret, *sub )

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,

strcmp( ++ret, sub+1 ) == 0 

ret - sub, true.

1 .

Answer 5

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Answer 6

char const *ret = sub;

int r = 0;
while ( ret = strchr( ret, *sub ) ) {

ret stores the address of the auxiliary array and in the while expression strchr(ret,*sub) comparing the value in subwith the address stored in ret whether it will work or not (is this comparison correct or not) please reply ...