diff --git a/src/boucane.cc b/src/boucane.cc
index 74dad9d..94f266f 100644
--- a/src/boucane.cc
+++ b/src/boucane.cc
@@ -1,11 +1,19 @@
 #include "boucane.hpp"
+#include "libs/string.hpp"
 
 extern "C" void boucane(){
     clear();
     char a[]="Loic Guegan";
     printk("Booting Boucane v%d.%d.%d",VERSION_MAJOR,VERSION_MINOR, VERSION_PATH);
 
+    char b[10];
+    substr(8, 9, a, b);
+    print("\n");
+    printk(b);
 
+    int gg=0;
+    gg+=((1>2) ? 1 : 0)+9;
+    printi(gg);
 
     while(1);
 }
\ No newline at end of file
diff --git a/src/drivers/framebuffer.cc b/src/drivers/framebuffer.cc
index b945e77..2fbe153 100644
--- a/src/drivers/framebuffer.cc
+++ b/src/drivers/framebuffer.cc
@@ -40,19 +40,19 @@ void putchar(char c){
 }
 
 void clear(){
-  for(char i=0;i<MAX_LINE;i++){
+  for(u8 i=0;i<MAX_LINE;i++){
     scrollup();
   }
 }
 
 void scrollup(){
   // Move VS.line up
-  for(char i=1;i<=MAX_LINE;i++){
-    for(char j=0;j<=MAX_COL;j++)
+  for(u8 i=1;i<=MAX_LINE;i++){
+    for(u8 j=0;j<=MAX_COL;j++)
       VS.mem[j*2+MAX_COL*(i-1)*2]=VS.mem[j*2+MAX_COL*i*2];
   }
   // Clear last VS.line
-  for(char i=0;i<=MAX_COL;i++){
+  for(u8 i=0;i<=MAX_COL;i++){
     VS.mem[i*2+MAX_COL*(MAX_LINE-1)*2]='\0';
   }
 }
diff --git a/src/libs/math.cc b/src/libs/math.cc
index 63487b2..27f009a 100644
--- a/src/libs/math.cc
+++ b/src/libs/math.cc
@@ -1,31 +1,31 @@
 #include "math.hpp"
 
-int pow(int x, int n) {
+u32 pow(u32 x, u32 n) {
   if (n < 0)
     return -1;
   else if (n == 0)
     return 1;
   else if (n == 1)
     return x;
-  int ret = x;
-  for (int i = 0; i < (n - 1); i++)
+  u32 ret = x;
+  for (u32 i = 0; i < (n - 1); i++)
     ret *= x;
   return ret;
 }
 
-int max(int x, int y) {
+u32 max(u32 x, u32 y) {
   if (x > y)
     return x;
   return y;
 }
 
-int min(int x, int y) {
+u32 min(u32 x, u32 y) {
   if (x < y)
     return x;
   return y;
 }
 
-int abs(int x) {
+u32 abs(u32 x) {
   if (x < 0)
     return -x;
   return x;
diff --git a/src/libs/math.hpp b/src/libs/math.hpp
index 1eaac1c..c5b7c46 100644
--- a/src/libs/math.hpp
+++ b/src/libs/math.hpp
@@ -1,6 +1,8 @@
 #pragma once
 
-int pow(int x, int n);
-int max(int x, int y);
-int min(int x, int y);
-int abs(int x);
+#include "core/types.hpp"
+
+u32 pow(u32 x, u32 n);
+u32 max(u32 x, u32 y);
+u32 min(u32 x, u32 y);
+u32 abs(u32 x);
diff --git a/src/libs/stdio.cc b/src/libs/stdio.cc
index 4a20c05..e73e4af 100644
--- a/src/libs/stdio.cc
+++ b/src/libs/stdio.cc
@@ -109,12 +109,12 @@ void printh(int h) {
   itoh(h, str);
   print(str);
 }
-void printh(int h, int size) {
+void printh(int h, u32 size) {
   char str[17];
   char str2[17];
   itoh(h, str);
-  int a = 0;
-  for (int i = min(max(16 - size, 0), 15); i < 16; i++) {
+  u32 a = 0;
+  for (u32 i = min(max(16 - size, 0), 15); i < 16; i++) {
     str2[a] = str[i];
     a++;
   }
diff --git a/src/libs/stdio.hpp b/src/libs/stdio.hpp
index f48ae81..fd266a5 100644
--- a/src/libs/stdio.hpp
+++ b/src/libs/stdio.hpp
@@ -33,4 +33,4 @@ void printh(int h);
 /**
  * Print an integer as hex using itoh() truncated to size
  */
-void printh(int h, int size);
+void printh(int h, u32 size);
diff --git a/src/libs/string.cc b/src/libs/string.cc
index f8ae3ca..73c3318 100644
--- a/src/libs/string.cc
+++ b/src/libs/string.cc
@@ -1,16 +1,16 @@
 #include "string.hpp"
 #include "math.hpp"
 
-void memcpy(void* src, void* dst, int size){
-    char *c_src=(char*)src;
-    char *c_dst=(char*)dst;
-    for(int i=0;i<size;i++)
-        *c_dst=*c_src;
+void memcpy(void* src, void* dst, u32 size){
+    u8 *c_src=(u8*)src;
+    u8 *c_dst=(u8*)dst;
+    for(u32 i=0;i<size;i++)
+        *(c_dst+i)=*(c_src+i);
 }
 
 void itoa(u64 i, char *a){
     // Check if lower than 0
-    char neg=0;
+    u8 neg=0;
     if(i<0){
         neg=1;
         i=-i;
@@ -18,17 +18,17 @@ void itoa(u64 i, char *a){
     }
 
     // Count number of digits
-    int len=1;
+    u32 len=1;
     while(i/pow(10,len)>=1)
     {
         len++;
     }
 
     // Build string
-    int max_pow=len-1;
-    for(int j=0;j<=max_pow;j++){
-        int cur_pow=pow(10,max_pow-j);
-        char digit=i/cur_pow;
+    u32 max_pow=len-1;
+    for(u32 j=0;j<=max_pow;j++){
+        u32 cur_pow=pow(10,max_pow-j);
+        u8 digit=i/cur_pow;
         a[j+neg]='0'+digit;
         i=i-digit*cur_pow; // Remove first digits (most significant)
     }
@@ -45,7 +45,7 @@ void itoh(u64 i, char *a){
     u32 i_a=i&0xFFFFFFFF;
     u32 i_b=i>>32;
 
-   for(char j=0;j<8;j++){
+   for(u8 j=0;j<8;j++){
         u64 t=(j*4);
         u64 mask=0xF;
         mask=mask <<  t;
@@ -53,7 +53,7 @@ void itoh(u64 i, char *a){
         a[15-j]=hex[index];
     } 
 
-   for(char j=0;j<8;j++){
+   for(u8 j=0;j<8;j++){
         u64 t=(j*4);
         u64 mask=0xF;
         mask=mask <<  t;
@@ -63,9 +63,15 @@ void itoh(u64 i, char *a){
     a[16]='\0';
 }
 
-int strlen(char *s){
-    int i=0;
+u32 strlen(char *s){
+    u32 i=0;
     while(s[i]!='\0')
         i++;
     return i;
+}
+
+void substr(u32 s, u32 e, char *src, char *dst){
+    u32 size=abs(e-s)+1;
+    memcpy(src+s, dst, size);
+    dst[size]='\0';
 }
\ No newline at end of file
diff --git a/src/libs/string.hpp b/src/libs/string.hpp
index 305b9a8..a7dce0a 100644
--- a/src/libs/string.hpp
+++ b/src/libs/string.hpp
@@ -5,7 +5,7 @@
 /**
  * Copy data byte per byte from src to dst
  */
-void memcpy(void *src, void *dst, int size);
+void memcpy(void *src, void *dst, u32 size);
 
 /**
  * Convert int to char array
@@ -20,4 +20,9 @@ void itoh(u64 i, char *a);
 /**
  * Length of a char*
  */
-int strlen(char *s);
+u32 strlen(char *s);
+
+/**
+ * Substr
+ */
+void substr(u32 s, u32 e, char *src, char *dst);