Longest Common Sub-Sequence implementation in C++

Problem : Given two sequence of elements (usually characters), find the longest subsequence present in both of them. A subsequence is a sequence that appears in the same order,as appeared in original sequence's  .

Example : Strings  "abc","abd","cde" are sub-sequence of string "abcdefghi".

Solution :  With dynamic programming we can solve this problem in O(m*n) time , where m is length of first sequence and n is length of second sequence.


C++ Solution  :

char *get_lcs(char *first_str,char *sec_str,int str_len1,int str_len2)
{
 int m,n,i,j;
 char temp_lcs[100][100];
 int temp_len_lcs[100][100];
 char ret_str[100];

 memset(temp_lcs,'\0',sizeof(temp_lcs));
 memset(temp_len_lcs,0,sizeof(temp_len_lcs));

 for(m = 0;m<str_len1;m++)
 {
  temp_len_lcs[m][0] = 0;
 }

 for(n = 0;n<str_len2+1;n++)
 {
  temp_len_lcs[0][n] = 0;
 }

 for(m = 0;m<str_len1;m++)
 {
  for(n = 1;n<str_len2+1;n++)
  {
   if(first_str[m] == sec_str[n-1])
   {
    temp_len_lcs[m][n] = temp_len_lcs[m-1][n-2] + 1;
    temp_lcs[m][n-1] = '=';
   }
   else
   {
    if(temp_len_lcs[m-1][n-1] >= temp_len_lcs[m][n-2])
    {
     temp_len_lcs[m][n-1] = temp_len_lcs[m-1][n-1];
     temp_lcs[m][n-1] = '+';
    }
    else
    {
     temp_len_lcs[m][n-1] = temp_len_lcs[m][n-2];
     temp_lcs[m][n-1] = '-';
    }
   }
  }
 }


 memset(ret_str,'\0',sizeof(ret_str));

 i = m;
 j = n;

 while(1)
 {
  if(i == 0 || j == 0)
  {
   break;
  }
  else
  {
   if(temp_lcs[i-1][j-1] == '=')
   {
    i--;
    j--;
    strncat(ret_str,(first_str+i),1);
 
   }
   else if(temp_lcs[i-1][j-1] == '+')
   {
    --i;
   }
   else
   {
    --j;
   }
  }
 }

 return strrev(ret_str);

}


Usage :
Call this function from main  like this

int main(void)
{
 char first_str[100];
 char sec_str[100];
 char lcs[100];

 memset(first_str,'\0',sizeof(first_str));
 memset(sec_str,'\0',sizeof(sec_str));
 memset(lcs,'\0',sizeof(lcs));

 scanf("%s",first_str);
 scanf("%s",sec_str);

 strcpy(lcs,get_lcs(first_str,sec_str,strlen(first_str),strlen(sec_str)));
 std::cout<<lcs<<"\n";

 int a;
 std::cin>>a;
 return 0;
}