How to express “if substring present in string do something” when using strstr?

Question

I am trying to write a very simple program, which takes a string of characters(amino acids, or nucleic acids) and checks how many times a sub-string appears and outputs the result.

However, I don't know how to state in the while if loop to add 1 to count only if there has been a match and to brake if it reaches end of the line. Since the output of strstr is a pointer towards the position of the match, I can't figure out how to express string equivalence as a logical condition for the if().

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

   int main(){

   int j,count; 
   char *i,dna_seq[50], desired_seq[3]="AT";  



   while(1){

     printf("\nPlease insert protein sequence:\n");
     gets(dna_seq);

     printf("\nPlease insert searched sequence:\n");
     gets(desired_seq);

     while(1){
       strstr(dna_seq,desired_seq);
         if(//**answer**//); 
         count++;
         dna_seq[j]++;
         if(i=='\0') break; 
      }   

     printf("\n\nOccurance of %s: %d times\n",desired_seq,count);
 }

}

Also what would you write for debugging (since I am trying to practice)?

Thank you in advance for the help, sorry if the question was not clearly posed.

Answer 1

strstr returns a pointer to the occurance of the string you're looking for, or NULL if it's not present. So you should loop until you get NULL , and every time you get a valid pointer, increment the counter, and start looking from right after it:

char* loc = NULL;
while (loc = strstr(prot_seq,desired_seq)) {
    count++;
    loc++;
}