Function to search for string in array of strings - c

Question

I am trying to write a function that searches for the unique part(maximum two characters) of a string in an array of strings. Although strstr and strchr are not working and crash my program for some reason. So I have resorted to trying to create something that resembles their function.
My question is this:
Why is strstr not working (something like strstr(lex[j],word)) and what am I doing wrong here?
Here is the code for the function that searches for two unique characters within an array of strings :
void convert(char word[])
{
int i;
for (i = 0 ; i <= strlen(word) ; i++)
{
if(word[i] >= 65 && word[i] <= 90)
{
word[i] = word[i]+32;
}
}
}
int twochar(char lex[50][50],char word[], int size,char temp[3])
{
int i,j,k,count,totlen;
convert(word);
for (i = 0 ; i < strlen(word) - 1 ; i++)
{
count = 0;
totlen = 0;
for(j = 0; j<size; j++)
{
convert(lex[j]);
totlen += strlen(lex[j]) - 1;
for(k = 0 ; k < strlen(lex[j]) - 1 ; k++)
{
if (word[i] != lex[j][k] || word[i+1] != lex[j][k + 1])
{
count++;
}
}
}
if(count = = totlen)
{
temp[0] = word[i];
temp[1] = word[i+1];
}
}
}
int main(int argc, char *argv[])
{
char lex[50][50] = {"word1","word2","word3","word4" }, word[] = "test";
char p[3];
twochar(lex,word,4,p);
printf("%c%c\n",p[0],p[1]);
return 0;
}

Answer 1

this line:
for(k=0;k<strlen(lex[j])-1;k++)
is the problem.
strlen(lex[0]) is 0
strlen(lex[0])-1 is -1 (0xFFFFFFFF in a 32 bit system)
k starts at 0 and is incremented until it is equal to 0xFFFFFFFF
of course, k exceeds the bounds of lex[0] when k = 50.
the result is undefined behaviour which leads to the seg fault event
To determine all the above, I compiled/linked the program via gcc, with the -ggdb parameter.
then I ran the program via 'gdb theprogram'
within gdb I entered
br main <-- break point set
run
c <-- continue
the program then crashed with a seg fault event
then I entered
bt <-- back trace
the bt showed me this line: 'if(word[i]!=lex[j][k] || word[i+1]!=lex[j] [k+1])'
Then I entered
p k <-- print variable k
=6832 (which is WAY out of bounds)
then I entered
run
y
br theprogram.c:41 (the line number from above) <-- set another break epoint
c
the program stopped at line 41
p j
=0 ( this was the gdb response )
p k
= 0
p i
= 0
a little thinking,
stepping though that inner loop using 'n' <-- next
and playing on gdb
indicated that the problem was in line 42
and resulted in revealing the root of the problem