/in/lab4.c: In function 'remove_element_by_index':
/in/lab4.c:88:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i = 0; i < len; i++)
                  ^
/in/lab4.c:90:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (i != index)
               ^~
/in/lab4.c: In function 'format_formula':
/in/lab4.c:123:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (i = 0; i < formula_len; i++)
                   ^
/in/lab4.c:148:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (i = 0; i < buf_len; i++)
                   ^
/in/lab4.c:151:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (is_number(buf[i]) && (i + 1 < buf_len) && is_operator(buf[i + 1]))
                                         ^
/in/lab4.c:155:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         else if (is_number(buf[i]) && (i + 1 < buf_len) && buf[i + 1] == ')')
                                              ^
/in/lab4.c:159:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         else if (is_number(buf[i]) && (i + 1 == buf_len))
                                              ^~
/in/lab4.c:163:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         else if (is_number(buf[i])&&(i+ 1 == buf_len-1))
                                           ^~
/in/lab4.c: In function 'get_postfix_formula':
/in/lab4.c:181:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (i = 0; i < formula_len; i++)
                   ^
/in/lab4.c: In function 'calculate':
/in/lab4.c:295:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (i = 0; i < formula_len; ++i) {
                   ^