diff --git a/docs/index.md b/docs/index.md
index 3f2aa70d..37e42dea 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -39,9 +39,11 @@
 
 * [`stdlib` module](stdlib/stdlib.md)
 
+* [`string` module](stdlib/string.md)
+
 * [Modules for reading input devices](stdlib/input.md)
 
-* [Other cross-platform modules](stdlib/other.md)
+* [Other cross-platform modules (`err`, `stdio`)](stdlib/other.md)
 
 * [Definitions available on only some platforms](stdlib/frequent.md)
 
diff --git a/docs/lang/preprocessor.md b/docs/lang/preprocessor.md
index 130a085c..5bd60d94 100644
--- a/docs/lang/preprocessor.md
+++ b/docs/lang/preprocessor.md
@@ -84,6 +84,10 @@ The following features are defined based on the chosen CPU and compilation optio
 
 * `CPM` – 1 if the target is CP/M, 0 otherwise
 
+* `NTSC` – 1 if the target is NTSC, 0 otherwise
+
+* `PAL` – 1 if the target is PAL, 0 otherwise
+
 ### Built-in preprocessor functions and operators
 
 The `defined` function returns 1 if the feature is defined, 0 otherwise.  
diff --git a/docs/stdlib/frequent.md b/docs/stdlib/frequent.md
index 1d855de7..79c3a4e8 100644
--- a/docs/stdlib/frequent.md
+++ b/docs/stdlib/frequent.md
@@ -16,6 +16,19 @@ Moves the cursor to the next line.
 
 Available for: all computer targets.
 
+#### `pointer readline()`
+
+Reads a line from the console and returns a pointer to a null-terminated string.
+The string is valid only until next read from the console.
+
+Available for: Commodore 64 with `c64_basic` module.
+
+#### `word readword()`
+
+Reads a 16-bit unsigned integer from the console.
+
+Available for: Commodore 64 with `c64_basic` module.
+
 #### `void bell()`
 
 Beeps.
diff --git a/docs/stdlib/other.md b/docs/stdlib/other.md
index c66f3114..2186335a 100644
--- a/docs/stdlib/other.md
+++ b/docs/stdlib/other.md
@@ -2,7 +2,7 @@
 
 ## stdio
 
-The `stdio` module automatically imports the `string` module.  
+The `stdio` module automatically imports the `string` and `err` modules.  
 It requires an implementation of `void putchar(byte a)` and therefore works only on targets with console output.
 
 #### `void putstr(pointer str, byte len)`
@@ -14,9 +14,13 @@ Prints a string of length `len` located at address `str`.
 Prints a null-terminated string located at address `str`.  
 If the string is longer than 255 bytes, then the behaviour is undefined (might even crash).
 
-## string
 
-#### `byte strzlen(pointer str)`
+## err
 
-Calculates the length of a null-terminated string.  
-If the string is longer than 255 bytes, then the behaviour is undefined (might even crash).
+#### `enum error_number`
+
+Standard error codes. All codes other than `err_ok` suggest that the last operation failed.
+
+#### `error_number errno`
+
+The result of the last operation.
diff --git a/docs/stdlib/string.md b/docs/stdlib/string.md
index e69de29b..2d72ef7f 100644
--- a/docs/stdlib/string.md
+++ b/docs/stdlib/string.md
@@ -0,0 +1,25 @@
+[< back to index](../index.md)
+
+## string
+
+The `string` module automatically imports the `err` module.  
+
+#### `byte strzlen(pointer str)`
+
+Calculates the length of a null-terminated string.  
+If the string is longer than 255 bytes, then the behaviour is undefined (might even crash).
+
+#### `sbyte strzcmp(pointer str1, pointer str2)`
+
+Compares two strings. Returns 0 if equal, non-0 if not equal.
+If any of the strings is longer than 255 bytes, then the behaviour is undefined (might even crash).
+
+#### `void strzcopy(pointer dest, pointer src)`
+
+Copies the source null-terminated string into the destination buffer.
+If the source string is longer than 255 bytes, then the behaviour is undefined (might even crash).
+
+#### `word strz2word(pointer str)`
+
+Converts a null-terminated string to a number.
+Sets `errno`.
diff --git a/examples/c64/calculator.mfk b/examples/c64/calculator.mfk
index 62dbc9e6..a8878cef 100644
--- a/examples/c64/calculator.mfk
+++ b/examples/c64/calculator.mfk
@@ -5,22 +5,25 @@ void main() {
     word a
     word b
 
-    putstrz("enter first number:{n}"z)
+    putstrz("enter first number:"z)
+    new_line()
     a = readword()
-    while readword_err != 0 {
-        putstrz("that wasn't a number, try again:{n}"z)
+    while errno != err_ok {
+        putstrz("that wasn't a number, try again:"z)
+        new_line()
         a = readword()
     }
 
     putstrz("enter second number:{n}"z)
     b = readword()
-    while readword_err != 0 {
-        putstrz("that wasn't a number, try again:{n}"z)
+    while errno != err_ok {
+        putstrz("that wasn't a number, try again:"z)
+        new_line()
         b = readword()
     }
 
-    putstrz("the sum is:{n}"z)
-    a += b
-    putword(a)
-    putchar(13)
+    putstrz("the sum is:"z)
+    new_line()
+    putword(a + b)
+    new_line()
 }
diff --git a/include/bbcmicro.ini b/include/bbcmicro.ini
index 0e65afb9..292e8d6a 100644
--- a/include/bbcmicro.ini
+++ b/include/bbcmicro.ini
@@ -20,6 +20,7 @@ KEYBOARD=1
 ; TODO: ?
 JOYSTICKS=1
 HAS_BITMAP_MODE=1
+PAL=1
 
 [output]
 style=single
diff --git a/include/c64_basic.mfk b/include/c64_basic.mfk
index bef806dd..5cd3634a 100644
--- a/include/c64_basic.mfk
+++ b/include/c64_basic.mfk
@@ -5,41 +5,26 @@
 #endif
 
 import c64_kernal
+import err
 
 // print a 16-bit number on the standard output
-asm void putword(word xa) @$BDCD extern
-asm void readline() @$A560 extern
+asm void putword_basic(word xa) @$BDCD extern
+
+//alias putword = putword_basic!
+
+asm void __readline_basic() @$A560 extern
+
+pointer readline_basic() {
+    __readline_basic()
+    return readline_out
+}
+
+alias readline = readline_basic!
+
 const pointer readline_out = $200
 
-byte readword_err
-
-word readword() {
-    readline()
-    readword_err = 0
-    word result
-    word four
-    result = 0
-    byte char
-    byte i
-    i = 0
-    while true {
-        char = readline_out[i]
-        if char == 0 {
-            if i == 0 {
-                readword_err = 1
-            }
-            return result
-        }
-        if 48 <= char <= 48+9 {
-            four = result
-            four <<= 2
-            result += four
-            result <<= 1
-            result += char - 48
-        } else {
-            readword_err = 1
-            return result
-        }
-        i += 1
-    }
+inline word readword_basic() {
+    return strz2word(readline_basic())
 }
+
+alias readword = readword_basic!
diff --git a/include/err.mfk b/include/err.mfk
new file mode 100644
index 00000000..fb478040
--- /dev/null
+++ b/include/err.mfk
@@ -0,0 +1,11 @@
+enum error_number {
+    err_ok
+    err_fail
+    err_numberformat
+    err_outofmemory
+    err_domain
+    err_range
+}
+
+
+error_number errno
diff --git a/include/pc88.ini b/include/pc88.ini
index a8305f17..3dc71942 100644
--- a/include/pc88.ini
+++ b/include/pc88.ini
@@ -19,6 +19,7 @@ KEYBOARD=1
 ; TODO:
 JOYSTICKS=1
 HAS_BITMAP_MODE=1
+NTSC=1
 
 [output]
 style=single
diff --git a/include/stdio.mfk b/include/stdio.mfk
index d3958453..ff5d084b 100644
--- a/include/stdio.mfk
+++ b/include/stdio.mfk
@@ -27,3 +27,28 @@ void putstrz(pointer str) {
 
 #endif
 
+void putword(word w) {
+    byte digits
+    byte lastdigit
+    digits = 0
+    word mask
+    for mask:[40000,4000,400,40,4] {
+        lastdigit = 0
+        while w >= mask {
+            w -= mask
+            lastdigit += 4
+        }
+        mask >>= 2
+        while w >= mask {
+            w -= mask
+            lastdigit += 1
+        }
+        if digits != 0 || lastdigit != 0 {
+            putchar('0' + lastdigit)
+            digits += 1
+        }
+    }
+    if digits == 0 {
+        putchar('0')
+    }
+}
diff --git a/include/stdlib.mfk b/include/stdlib.mfk
index 29a8b16b..53b64ab5 100644
--- a/include/stdlib.mfk
+++ b/include/stdlib.mfk
@@ -7,3 +7,7 @@ import stdlib_i80
 #else
 #warn Unsupported architecture
 #endif
+
+#if PAL && NTSC
+#warn PAL and NTSC enabled simultaneously
+#endif
diff --git a/include/stdlib_6502.mfk b/include/stdlib_6502.mfk
index 5173b7e7..73efc8dd 100644
--- a/include/stdlib_6502.mfk
+++ b/include/stdlib_6502.mfk
@@ -29,7 +29,7 @@ asm byte hi_nibble_to_hex(byte a) {
     LSR
     LSR
     LSR
-    JMP lo_nibble_to_hex
+    ? JMP lo_nibble_to_hex
 }
 
 asm byte lo_nibble_to_hex(byte a) {
@@ -40,7 +40,7 @@ asm byte lo_nibble_to_hex(byte a) {
     BCC _lo_nibble_to_hex_lbl
     ADC #$6 // carry is set
 _lo_nibble_to_hex_lbl:
-    RTS
+    ? RTS
 }
 
 macro asm void panic() {
diff --git a/include/string.mfk b/include/string.mfk
index 69b5de45..b2783d36 100644
--- a/include/string.mfk
+++ b/include/string.mfk
@@ -1,23 +1,39 @@
+import err
 
 #if ARCH_I80
-
-byte strzlen(pointer str) {
-    pointer end
-    end = str
-    while end[0] != 0 {
-        end += 1
-    }
-    return lo(end - str)
-}
-
+import string_fastpointers
 #else
+import string_fastindices
+#endif
 
-byte strzlen(pointer str) {
-    byte index
-    index = 0
-    while str[index] != 0 {
-        index += 1
+
+word strz2word(pointer str) {
+    byte i
+    byte char
+    word next
+    word result
+    result = 0
+    i = 0
+    errno = err_ok
+    while true {
+        char = str[i]
+        if char == 0 {
+            if i == 0 {
+                errno = err_numberformat
+            }
+            return result
+        }
+        if '0' <= char <= '0' + 9 {
+            next = result * 10
+            next += char - '0'
+            if next < result {
+                errno = err_range
+            }
+            result = next
+        } else {
+            errno = err_numberformat
+            return result
+        }
+        i += 1
     }
-    return index
 }
-#endif
\ No newline at end of file
diff --git a/include/string_fastindices.mfk b/include/string_fastindices.mfk
new file mode 100644
index 00000000..28bcba8f
--- /dev/null
+++ b/include/string_fastindices.mfk
@@ -0,0 +1,37 @@
+byte strzlen(pointer str) {
+    byte index
+    index = 0
+    while str[index] != 0 {
+        index += 1
+    }
+    return index
+}
+
+sbyte strzcmp(pointer str1, pointer str2) {
+    byte i1
+    byte i2
+    i1 = 0
+    i2 = 0
+    while true {
+        if str1[i1] != str2[i2] {
+            if str1[i1] < str2[i2] { return -1 }
+            return 1
+        }
+        if str1[i1] == 0 {
+            return 0
+        }
+        i1 += 1
+        i2 += 1
+    }
+}
+
+void strzcopy(pointer dest, pointer src) {
+    byte i
+    byte c
+    i = 0
+    do {
+        c = src[i]
+        dest[i] = c
+        i += 1
+    } while c != 0
+}
diff --git a/include/string_fastpointers.mfk b/include/string_fastpointers.mfk
new file mode 100644
index 00000000..87047bd7
--- /dev/null
+++ b/include/string_fastpointers.mfk
@@ -0,0 +1,37 @@
+#pragma zilog_syntax
+
+byte strzlen(pointer str) {
+    pointer end
+    end = str
+    while end[0] != 0 {
+        end += 1
+    }
+    return lo(end - str)
+}
+
+sbyte strzcmp(pointer str1, pointer str2) {
+    while true {
+        if str1[0] == 0 {
+            if str2[0] == 0 {
+                return 0
+            } else {
+                return -1
+            }
+        } else if str1[0] != str2[0] {
+            if str1[0] < str2[0] { return -1 }
+            return 1
+        }
+        str1 += 1
+        str2 += 1
+    }
+}
+
+void strzcopy(pointer dest, pointer src) {
+    byte c
+    do {
+        c = src[0]
+        dest[0] = c
+        src += 1
+        dest += 1
+    } while c != 0
+}
diff --git a/src/main/scala/millfork/env/Environment.scala b/src/main/scala/millfork/env/Environment.scala
index dc6ad32e..09417537 100644
--- a/src/main/scala/millfork/env/Environment.scala
+++ b/src/main/scala/millfork/env/Environment.scala
@@ -353,7 +353,7 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
     addThing(ConstantThing("true", NumericConstant(1, 0), trueType), None)
     addThing(ConstantThing("false", NumericConstant(0, 0), falseType), None)
     addThing(ConstantThing("__zeropage_usage", UnexpandedConstant("__zeropage_usage", 1), b), None)
-    addThing(ConstantThing("__heap_start", UnexpandedConstant("__heap_start", 1), b), None)
+    addThing(ConstantThing("__heap_start", UnexpandedConstant("__heap_start", 2), p), None)
     addThing(ConstantThing("$0000", NumericConstant(0, 2), p), None)
     addThing(FlagBooleanType("set_carry",
       BranchingOpcodeMapping(Opcode.BCS, IfFlagSet(ZFlag.C)),