c - Issue finding number of occurrences of a given substring in a string -

the below code returns number of matching sub strings zero.there no errors in code , not sure have gone wrong logically.

#include<stdio.h> #include<string.h>  int main() {      int i,j,len ,k ,count, num ;     char str[100],sub[100],comp[100] ;      // sub sub string .     printf("please enter string") ;      gets(str) ;     printf("enter substring searched for") ;     gets(sub) ;     len=strlen(sub) ;     ( i=0 ; < strlen(str) - len ; i++ )      //goes till length of string - length of sub string characters can compared.       {            num = + len ;          ( j=i,k=0 ; j<num ; j++, k++ )          //loop store each sub string in array comp.            {              comp[k]=str[j] ;            }          if ( strcmp(comp,sub) == 0 )             { count++ ; }      }     printf("no of occurances is:%d",count) ;     return 0 ; }   

as mentioned in comments, when constructing comp, you're not adding terminating null byte @ end. because rest of comp not initialized, invoke undefined behavior when calling strcmp.

add null byte @ end of inner for loop fix problem:

     ( j=i,k=0 ; j<num ; j++, k++ )      //loop store each sub string in array comp.        {          comp[k]=str[j] ;        }      comp[k] = '\0'; 

actually, rather creating separate substring, use strncmp, compares number of characters:

for ( i=0 ; < strlen(str) - len ; i++ )  //goes till length of string - length of sub string characters can compared.   {        if ( strncmp(&str[i],sub,strlen(sub)) == 0 )         { count++ ; }  } 

also, don't use gets, prone buffer overflows. use fgets instead.