diff --git a/src/Hashtable/Hashtable.c b/src/Hashtable/Hashtable.c
index ae84083..9c8fe15 100644
--- a/src/Hashtable/Hashtable.c
+++ b/src/Hashtable/Hashtable.c
@@ -86,7 +86,7 @@ Unitype* Hashtable_getPtr(Hashtable* ht, char* key){
     u32 arlen=Autoarr_length(ar);
     for(u32 i=0;i<arlen;i++){
         KVPair* p=Autoarr_getPtr(ar,i);
-        if(cptr_compare(key,p->key)) return &p->value;
+        if(cptr_equals(key,p->key)) return &p->value;
     }
     return NULL;
 }
@@ -96,7 +96,7 @@ Unitype Hashtable_get(Hashtable* ht, char* key){
     u32 arlen=Autoarr_length(ar);
     for(u32 i=0;i<arlen;i++){
         KVPair p=Autoarr_get(ar,i);
-        if(cptr_compare(key,p.key)) return p.value;
+        if(cptr_equals(key,p.key)) return p.value;
     }
     return UniNull;
 }
diff --git a/src/base/cptr.c b/src/base/cptr.c
index 5c5436e..5876d1a 100644
--- a/src/base/cptr.c
+++ b/src/base/cptr.c
@@ -1,15 +1,17 @@
 #include "base.h"
+#include "../String/StringBuilder.h"
 #include <ctype.h>
 
 // returns length of char buffer (without \0)
-u32 cptr_length(char* str){
-    u32 len=0;
-    while(*(str++)) len++;
-    return len;
+u32 cptr_length(const char* str){
+    const char *const str_first=str;
+    while(*str)
+        str++;
+    return str-str_first;
 }
 
 // allocates new char[] and copies src there
-char* cptr_copy(char* src){
+char* cptr_copy(const char* src){
     u32 len=cptr_length(src)+1;
     char* dst=malloc(len);
     while(len--!=0)
@@ -17,16 +19,6 @@ char* cptr_copy(char* src){
     return dst;
 }
 
-// compares two char buffers, NullPtr-friendly
-bool cptr_compare(char* key0, char* key1){
-    if(!key0) return key1 ? false : true;
-    if(!key1) return false;
-    while(*key0&&*key1)
-        if(*key0++ != *key1++) 
-            return false;
-    return true;
-}
-
 // multiplies char n times
 char* char_multiply(char c, u32 n){
     char* rez=malloc(n+1);
@@ -36,63 +28,105 @@ char* char_multiply(char c, u32 n){
     return rez;
 }
 
-bool cptr_startsWith(char* ptr, char* fragment){
-    for(char cs=*ptr, cf=*fragment; cf; cs=*++ptr, cf=*++fragment)
-        if(cs!=cf) return false;
-    return true;
+bool cptr_equals(const char* key0, const char* key1){
+    char c0=*key0;
+    char c1=*key1;
+    bool eq=c0==c1;
+    while(c0 && c1 && eq) {
+        c0=*++key0;
+        c1=*++key1;
+        eq=c0==c1;
+    }
+    return eq;
 }
 
-bool cptr_endsWith(char* ptr, char* fragment){
-    ptr+=cptr_length(ptr)-cptr_length(fragment);
-    for(char cs=*ptr, cf=*fragment; cf; cs=*++ptr, cf=*++fragment)
-        if(cs!=cf) return false;
-    return true;
+bool cptr_startsWith(const char* src, const char* fragment){
+    char c0=*src;
+    char c1=*fragment;
+    bool eq=c0==c1 && c0 !=0 && c1!=0;
+    while(c0 && c1 && eq) {
+        c0=*++src;
+        c1=*++fragment;
+        eq=c0==c1;
+        if(c1==0)
+            return true;
+    }
+    return eq;
 }
 
-u32 cptr_indexOf(char* ptr, char* fragment){
-    char sc=*ptr;
-    for(u32 si=0, fi=0; sc!='\0'; si++){
-        sc=ptr[si];
-        if(sc==fragment[fi]){
-            fi++;
-            if(fragment[fi]==0)
-                return si-fi+1;
-        }
-        else fi=0;
+bool cptr_endsWith(const char* src, const char* fragment){
+    u32 src_len=cptr_length(src);
+    u32 fr_len=cptr_length(fragment);
+    if(src_len<fr_len || src_len==0 || fr_len==0)
+        return false;
+    src+=src_len-fr_len;
+    return cptr_equals(src, fragment);
+}
+
+
+i32 cptr_seek(const char* src, const char* fragment, u32 startIndex, u32 seekLength){
+    char sc=*src, fc=*fragment;
+    if(sc==0 || fc==0)
+        return -1;
+    u32 fr_start=startIndex;
+    for(u32 si=startIndex; si-startIndex<seekLength && sc!=0; si++){
+        sc=src[si];
+        fc=fragment[si-fr_start];
+        if(fc==0)
+            return fr_start;
+        if(sc!=fc)
+            fr_start++;
     }
     return -1;
 }
-u32 cptr_indexOfChar(char* ptr, char fragment){
-    char sc=*ptr;
-    for(u32 si=0; sc!='\0'; si++){
-        sc=ptr[si];
-        if(sc==fragment){
+
+i32 cptr_seekReverse(const char* src, const char* fragment, u32 startIndex, u32 seekLength){
+    char sc=*src, fc=*fragment;
+    if(sc==0 || fc==0)
+        return -1;
+    i32 len=cptr_length(src);
+    if(startIndex==(u32)-1)
+        startIndex=len-1;
+    u32 fr_len=cptr_length(fragment);
+    for(u32 si=startIndex; si<(u32)-1 && si!=len-1-seekLength; si--){
+        if(si+1<fr_len)
+            return -1;
+        sc=src[si];
+        fc=fragment[0];
+        u32 fr_start=si;
+        for(u32 fi=0; fc==sc ; fi++){
+            if(fi==fr_len)
+                return fr_start;
+            fc=fragment[fi];
+            sc=src[si--];
+        }
+    }
+    return -1;
+}
+
+i32 cptr_seekChar(const char* src, char fragment, u32 startIndex, u32 seekLength){
+    char sc=*src;
+    if(sc==0 || fragment==0)
+        return -1;
+    for(u32 si=startIndex; si-startIndex<seekLength && sc!=0; si++){
+        sc=src[si];
+        if(sc==fragment)
             return si;
-        }
     }
     return -1;
 }
-u32 cptr_lastIndexOf(char* ptr, char* fragment){
-    char sc;
-    u32 fi_last=cptr_length(fragment)-1;
-    for(i32 si=cptr_length(ptr)-1, fi=fi_last; si>=0; si--){
-        sc=ptr[si];
-        if(sc==fragment[fi]){
-            if(fi==0)
-                return si;
-            fi--;
-        }
-        else fi=fi_last;
-    }
-    return -1;
-}
-u32 cptr_lastIndexOfChar(char* ptr, char fragment){
-    char sc;
-    for(i32 si=cptr_length(ptr)-1; si>=0; si--){
-        sc=ptr[si];
-        if(sc==fragment){
+
+i32 cptr_seekCharReverse(const char* src, char fragment, u32 startIndex, u32 seekLength){
+    char sc=*src;
+    if(sc==0 || fragment==0)
+        return -1;
+    i32 len=cptr_length(src);
+    if(startIndex==(u32)-1)
+        startIndex=len-1;
+    for(u32 si=startIndex; si<(u32)-1 && si!=len-1-seekLength; si--){
+        sc=src[si];
+        if(sc==fragment)
             return si;
-        }
     }
     return -1;
 }
@@ -123,7 +157,7 @@ char* __cptr_concat(u32 n, ...){
 
     // allocating memory for output value
     char* totality=malloc(totalLength+1);
-    const char* output=totality;
+    char* output=totality;
     totality[totalLength]=0;
     
     // copying content of all strings to rezult
@@ -137,7 +171,7 @@ char* __cptr_concat(u32 n, ...){
     return output;
 }
 
-char* cptr_toLower(char* src) {
+char* cptr_toLower(const char* src) {
     u32 length=cptr_length(src);
     char *p=malloc(length+1);
     p[length]=0;
@@ -146,7 +180,7 @@ char* cptr_toLower(char* src) {
     return p;
 }
 
-char* cptr_toUpper(char* src) {
+char* cptr_toUpper(const char* src) {
     u32 length=cptr_length(src);
     char *p=malloc(length+1);
     p[length]=0;
@@ -154,3 +188,28 @@ char* cptr_toUpper(char* src) {
         p[i]=toupper(src[i]);
     return p;
 }
+
+char* cptr_replaceChar(const char* src, char c_old, char c_new, u32 startIndex, u32 seekLength){
+    char* rzlt=cptr_copy(src);
+    char c=*src;
+    for(u32 i=startIndex; i<seekLength && c!=0; i++, src++){
+        if(c==c_old)
+            *rzlt=c_new;
+    }
+    return rzlt;
+}
+
+char* cptr_replace(const char* src, char* str_old, char* str_new, u32 startIndex, u32 seekLength){
+    StringBuilder* sb=StringBuilder_create();
+    const u32 str_old_len=cptr_length(str_old);
+    const u32 str_new_len=cptr_length(str_new);
+    i32 i=startIndex;
+    while( (i=cptr_seek(src, str_old, i, -1)) !=-1 ){
+        if(i!=0)
+            StringBuilder_append_string(sb, (string){.ptr=(char*)src, .length=i});
+        StringBuilder_append_string(sb, (string){.ptr=str_new, .length=str_new_len});
+        src+=i+str_old_len;
+    }
+    string rezult=StringBuilder_build(sb);
+    return rezult.ptr;
+}
diff --git a/src/base/cptr.h b/src/base/cptr.h
index 55c2a39..fe15bed 100644
--- a/src/base/cptr.h
+++ b/src/base/cptr.h
@@ -7,39 +7,63 @@ extern "C" {
 #include "std.h"
 
 // returns length of char buffer (without \0)
-u32 cptr_length(char* str);
+u32 cptr_length(const char* str);
 
 // allocates new char[] and copies src there
-char* cptr_copy(char* src);
+char* cptr_copy(const char* src);
 
-// compares two char buffers, NullPtr-friendly
-bool cptr_compare(char* key0, char* key1);
+bool cptr_equals(const char* key0, const char* key1);
+
+bool cptr_startsWith(const char* src, const char* fragment);
+
+bool cptr_endsWith(const char* src, const char* fragment);
 
 // multiplies char n times
 char* char_multiply(char c, u32 n);
 
-bool cptr_startsWith(char* ptr, char* fragment);
+/// @param startIndex 0 ... src length 
+/// @param seekLength 0 ... -1
+/// @return pos of first <fragment> inclusion in <src> or -1 if not found
+i32 cptr_seek(const char* src, const char* fragment, u32 startIndex, u32 seekLength);
 
-bool cptr_endsWith(char* ptr, char* fragment);
+/// @param startIndex -1 ... src length
+/// @param seekLength 0 ... -1
+/// @return pos of first <fragment> inclusion in <src> or -1 if not found
+i32 cptr_seekReverse(const char* src, const char* fragment, u32 startIndex, u32 seekLength);
+
+/// @param startIndex 0 ... src length
+/// @param seekLength 0 ... -1
+/// @return pos of first <fragment> inclusion in <src> or -1 if not found
+i32 cptr_seekChar(const char* src, char fragment, u32 startIndex, u32 seekLength);
+
+/// @param startIndex -1 ... src length
+/// @param seekLength 0 ... -1
+/// @return pos of first <fragment> inclusion in <src> or -1 if not found
+i32 cptr_seekCharReverse(const char* src, char fragment, u32 startIndex, u32 seekLength);
 
 /// @brief search for <fragment> in <ptr>
 /// @return index of first <fragment> inclusion or -1 if not found
-u32 cptr_indexOf(char* ptr, char* fragment);
+static inline i32 cptr_indexOf(const char* src, const char* fragment)
+{ return cptr_seek(src, fragment, 0, -1); }
+
 /// @brief search for <fragment> in <ptr>
 /// @return index of first <fragment> inclusion or -1 if not found
-u32 cptr_indexOfChar(char* ptr, char fragment);
-/// @brief search for <fragment> in <ptr>
-/// @return index of last <fragment> inclusion or -1 if not found
-u32 cptr_lastIndexOf(char* ptr, char* fragment);
-/// @brief search for <fragment> in <ptr>
-/// @return index of last <fragment> inclusion or -1 if not found
-u32 cptr_lastIndexOfChar(char* ptr, char fragment);
+static inline i32 cptr_indexOfChar(const char* src, char fragment)
+{ return cptr_seekChar(src, fragment, 0, -1); }
 
-static inline bool cptr_contains(char* ptr, char* fragment){
-    // if(cptr_indexOf(ptr, fragment)==-1)
-    //     return false;
-    // return true;
-    return cptr_indexOf(ptr, fragment) +1;
+/// @brief search for <fragment> in <ptr>
+/// @return index of last <fragment> inclusion or -1 if not found
+static inline i32 cptr_lastIndexOf(const char* src, const char* fragment)
+{ return cptr_seekReverse(src, fragment, -1, -1); }
+
+/// @brief search for <fragment> in <ptr>
+/// @return index of last <fragment> inclusion or -1 if not found
+static inline i32 cptr_lastIndexOfChar(const char* src, char fragment)
+{ return cptr_seekCharReverse(src, fragment, -1, -1); }
+
+
+static inline bool cptr_contains(const char* src, const char* fragment){
+    return cptr_seek(src, fragment, 0, -1) +1;
 }
 
 void memcopy(void* from, void* to, u32 size);
@@ -47,8 +71,17 @@ void memcopy(void* from, void* to, u32 size);
 char* __cptr_concat(u32 n, ...);
 #define cptr_concat(STR...) __cptr_concat(count_args(STR), STR)
 
-char* cptr_toLower(char* src);
-char* cptr_toUpper(char* src);
+char* cptr_toLower(const char* src);
+char* cptr_toUpper(const char* src);
+
+/// @param startIndex 0 ... src length
+/// @param seekLength 0 ... -1
+/// @return <src> with <str_old> replaced by <str_new> or empty cstring if <str_old> not found
+char* cptr_replace(const char* src, char* str_old, char* str_new, u32 startIndex, u32 seekLength);
+/// @param startIndex 0 ... src length
+/// @param seekLength 0 ... -1
+/// @return <src> with <c_old> replaced by <c_new> or empty cstring if <str_old> not found
+char* cptr_replaceChar(const char* src, char c_old, char c_new, u32 startIndex, u32 seekLength);
 
 #if __cplusplus
 }
diff --git a/tests/test_cptr.c b/tests/test_cptr.c
new file mode 100644
index 0000000..ff05f4e
--- /dev/null
+++ b/tests/test_cptr.c
@@ -0,0 +1,161 @@
+#include "tests.h"
+
+/*
+        TODO
+test cptr_seek...
+test cptr_...indexOf... 
+test cptr_replace...
+
+cases:
+*/
+
+const char* strings[]={
+    "",
+    "abab",
+    "ab_ab",
+    "abab_",
+    "_abab",
+    "_ab_ab_",
+    "_ab_ab",
+    "_abab_",
+    "_ab_ab_",
+    "str_not_containing_a_b",
+    ""
+};
+
+#define test_startsWith(str, fragm) \
+    kprintf("\e[37m'"str"' starts with '"fragm"'"); \
+    if(cptr_startsWith(str,fragm)) kprintf("\e[92m true\n"); \
+    else { kprintf("\e[91m false\n"); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_DoesntStartWith(str, fragm) \
+    kprintf("\e[37m'"str"' doesnt start with '"fragm"'"); \
+    if(!cptr_startsWith(str,fragm)) kprintf("\e[92m true\n"); \
+    else { kprintf("\e[91m false\n"); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_endsWith(str, fragm) \
+    kprintf("\e[37m'"str"' ends with '"fragm"'"); \
+    if(cptr_endsWith(str,fragm)) kprintf("\e[92m true\n"); \
+    else { kprintf("\e[91m false\n"); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_DoesntEndWith(str, fragm) \
+    kprintf("\e[37m'"str"' doesnt end with '"fragm"'"); \
+    if(!cptr_endsWith(str,fragm)) kprintf("\e[92m true\n"); \
+    else { kprintf("\e[91m false\n"); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_seekChar(str, fragm, start, count, expected) \
+    kprintf("\e[37mseek "#fragm" in '"str"' startIndex "#start" count "#count); \
+    pos=cptr_seekChar(str, fragm, start, count); \
+    if(pos == expected) kprintf("\e[92m %i\n", pos); \
+    else { kprintf("\e[91m %i\n", pos); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_seekCharReverse(str, fragm, start, count, expected) \
+    kprintf("\e[37mseek reverse "#fragm" in '"str"' startIndex "#start" count "#count); \
+    pos=cptr_seekCharReverse(str, fragm, start, count); \
+    if(pos == expected) kprintf("\e[92m %i\n", pos); \
+    else { kprintf("\e[91m %i\n", pos); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_seek(str, fragm, start, count, expected) \
+    kprintf("\e[37mseek '"fragm"' in '"str"' startIndex "#start" count "#count); \
+    pos=cptr_seek(str, fragm, start, count); \
+    if(pos == expected) kprintf("\e[92m %i\n", pos); \
+    else { kprintf("\e[91m %i\n", pos); throw(ERR_UNEXPECTEDVAL); }
+
+#define test_seekReverse(str, fragm, start, count, expected) \
+    kprintf("\e[37mseek reverse '"fragm"' in '"str"' startIndex "#start" count "#count); \
+    pos=cptr_seekReverse(str, fragm, start, count); \
+    if(pos == expected) kprintf("\e[92m %i\n", pos); \
+    else { kprintf("\e[91m %i\n", pos); throw(ERR_UNEXPECTEDVAL); }
+
+const int strings_len=sizeof(strings)/sizeof(strings[0]);
+
+void test_cptr(){
+    // optime(__func__,1,
+        kprintf("\e[96m-------------[test_cptr]--------------\n");
+        // compare
+        kprintf("\e[94m--------------[compare]---------------\n");
+        for(int i=0; i<strings_len-1; i++){
+            // != next
+            kprintf("\e[37m'%s'!='%s'", strings[i], strings[i+1]);
+            bool not_eq= ! cptr_equals(strings[i],strings[i+1]);
+            if(not_eq) kprintf("\e[92m true\n");
+            else {
+                kprintf("\e[91m false\n");
+                throw(ERR_UNEXPECTEDVAL);
+            }
+            // == self
+            kprintf("\e[37m'%s'=='%s'", strings[i], strings[i]);
+            bool eq=cptr_equals(strings[i],strings[i]);
+            if(eq) kprintf("\e[92m true\n");
+            else {
+                kprintf("\e[91m false\n");
+                throw(ERR_UNEXPECTEDVAL);
+            }
+        }
+        
+        kprintf("\e[94m-------------[startsWith]-------------\n");
+        test_startsWith("abab","ab");
+        test_startsWith("abab","abab");
+        test_DoesntStartWith("","");
+        test_DoesntStartWith("abab","ababc");
+        test_DoesntStartWith("abab","");
+        test_DoesntStartWith("","abab");
+        
+        kprintf("\e[94m--------------[endsWith]--------------\n");
+        test_endsWith("cab","ab");
+        test_endsWith("abab","abab");
+        test_DoesntEndWith("","");
+        test_DoesntEndWith("abab","ababc");
+        test_DoesntEndWith("abab","");
+        test_DoesntEndWith("","abab");
+
+        i32 pos=-1;
+        kprintf("\e[94m--------------[seekChar]--------------\n");
+        test_seekChar("", '\0', 0, -1, -1)
+        test_seekChar("", 'u', 0, -1, -1)
+        test_seekChar("ab", '\0', 0, -1, -1)
+        test_seekChar("ab", 'u', 0, -1, -1)
+        test_seekChar("ab", 'a', 0, -1, 0)
+        test_seekChar("ab", 'b', 0, -1, 1)
+        test_seekChar("ab", '\0', 0, 2, -1)
+        test_seekChar("ab", 'b', 1, 2, 1)
+        test_seekChar("ab", 'b', 1, 1, 1)
+        
+        kprintf("\e[94m----------[seekCharReverse]-----------\n");
+        test_seekCharReverse("", 'u', 0, -1, -1)
+        test_seekCharReverse("ab", 'u', 0, -1, -1)
+        test_seekCharReverse("ab", 'a', 0, -1, 0)
+        test_seekCharReverse("ab", 'b', 1, -1, 1)
+        test_seekCharReverse("ab", 'a', -1, -1, 0)
+        test_seekCharReverse("ab", 'b', -1, -1, 1)
+        test_seekCharReverse("ab", '\0', -1, -1, -1)
+        test_seekCharReverse("ab", '\0', 2, 2, -1)
+        test_seekCharReverse("ab", 'b', 1, 2, 1)
+        test_seekCharReverse("ab", 'b', 1, 1, 1)
+        
+        kprintf("\e[94m----------------[seek]----------------\n");
+        test_seek("", "", 0, -1, -1)
+        test_seek("", "u", 0, -1, -1)
+        test_seek("ab", "", 0, -1, -1)
+        test_seek("ab", "u", 0, -1, -1)
+        test_seek("ab", "a", 0, -1, 0)
+        test_seek("ab", "b", 0, -1, 1)
+        test_seek("ab", "ab", 0, -1, 0)
+        test_seek("ab_ab", "ab", 0, -1, 0)
+        test_seek("ab_ab", "ab", 1, -1, 3)
+        test_seek("ab_ab", "ab", 1, 5, 3)
+        test_seek("ab_ab", "ab", 1, 4, -1)
+        
+        kprintf("\e[94m------------[seekReverse]-------------\n");
+        test_seekReverse("", "u", 0, -1, -1)
+        test_seekReverse("ab", "u", 0, -1, -1)
+        test_seekReverse("ab", "a", 0, -1, 0)
+        test_seekReverse("ab", "b", 1, -1, 1)
+        test_seekReverse("ab", "a", -1, -1, 0)
+        test_seekReverse("ab", "b", -1, -1, 1)
+        test_seekReverse("ab", "", -1, -1, -1)
+        test_seekReverse("ab", "", 2, 2, -1)
+        test_seekReverse("ab", "b", 1, 2, 1)
+        test_seekReverse("ab", "b", 1, 1, 1)
+    // );
+}
\ No newline at end of file
diff --git a/tests/tests.h b/tests/tests.h
index 2788cac..b3cc22f 100644
--- a/tests/tests.h
+++ b/tests/tests.h
@@ -6,6 +6,7 @@
 extern "C" {
 #endif
 
+void test_cptr();
 void test_string();
 void test_safethrow();
 void test_searchtree();
@@ -21,7 +22,8 @@ void test_type_system();
 
 inline void test_all(){
     kprintf("\e[97mkerep tests are starting!\n");
-    optime(__func__, 1, 
+    optime(__func__, 1,
+        test_cptr();
         test_type_system();
         test_string();
         test_safethrow();