Printing a Count in C Only Printing to 65 - c

Question

I am trying to make a very simple 64 bit operating system, and so far have done really well, but since I am not very familiar with C I have been having some problems with it, and this one stumped me. The output would count like normal (1 2 3 4 5 6 7 8 9 10 11 12 etc.) but it would stop printing at 65. I know that "print.h" works because I have tested it many times, but I am not so sure on my method of converting the numbers to a character array. Any help at all would be much appreciated. Here's my code:
#include "print.h"
int getLen(int x) {
unsigned int n = x;
int count = 0;
while(n!=0)
{
n=n/10;
count++;
}
return count;
}
char ITC(unsigned int x) {
char ret;
unsigned int n = x;
if(n==0){
ret='0';
}
if(n==1){
ret='1';
}
if(n==2){
ret='2';
}
if(n==3){
ret='3';
}
if(n==4){
ret='4';
}
if(n==5){
ret='5';
}
if(n==6){
ret='6';
}
if(n==7){
ret='7';
}
if(n==8){
ret='8';
}
if(n==9){
ret='9';
}
return ret;
}
void kernel_main(){
print_clear();
print_set_color(PRINT_COLOR_GREEN, PRINT_COLOR_BLACK);
char out[512];
int onOut = 0;
for (int i = 0; i < 100; i++)
{
onOut++;
unsigned int n = i;
while (n != 0) {
out[onOut + getLen(n)] = ITC(n%10);
n /= 10;
}
out[onOut + getLen(i) + 1] = '\n';
onOut += getLen(i) + 1;
}
for (int i = 0; i < 512; i++)
{
print_char(out[i]);
}
}

Answer 1

The issue is with the algorithm rather then perhaps familiarity with C. Your indexing into the unitialised out array was leaving gaps so outputting junk that happened to be in the array.
Consider the following - the parts I changed annotated - not all are part of the solution; just good practice:
char out[512] = {0}; // <<< Good idea to initialise
int onOut = 0;
for (int i = 1; i < 100; i++) // Start form 1 not zero
{
int n = i; // <<< Type agreement with i
int numlen = getLen(n) ; // <<< Get the length of the initial number
// Don't unnecessarily calculate in the loop
// when you know it decrements by 1 on each
// iteration
for( int j = onOut + numlen; // <<< Start from the end position
(n!=0) && j >= onOut; // <<< toward the start position
j-- ) // <<< backward
{
out[j - 1] = ITC(n % 10); // <<< Insert digit, starting from index zero
n /= 10;
}
onOut += numlen ; // <<< Move to end of newly inserted number
out[onOut++] = '\n'; // <<< Add the newline
}
Note that you have over-complicated this code somewhat; especially w.r.t. to ITC() if you code like that habitually your "operating system" will run very slowly. ITC() can be reduced to a simple look-up thus:
char ITC(unsigned int x)
{
static const char digits[] = "0123456789" ;
return digits[x] ;
}
Or in any likely character set where digits are contiguous and in order, arithmetically thus:
char ITC(unsigned int x)
{
return '0' + x ;
}
I'd give two pieces of advice for success in this project and programming in general.
Comment your code. If you have to explain it to yourself, you are more likely to find the flaws. But also later maintainers or people assisting you with debugging will have an idea of your intended semantics.
Use a debugger. I used a debugger to figure out were your code was going wrong because it was quicker and more direct that other methods. Certainly quicker than posting questions of StackOverflow!

Answer 2

I don't understand why you make that one function so complicated, what's wrong with this?
char ITC(unsigned int x) {
return (char)((int)'0' + n);
}

Answer 3

Some of the above comments are correct, plus you also need to terminate your string with a null character... and NOT print all 512 characters of a non-initialized array. Something like this should work much better (though you should also include the contents of print.h so we can see if there are any problems there):
#include "print.h"
int getLen(unsigned int x)
{
int count = 0;
while (n != 0) {
n = n / 10;
count++;
}
return count;
}
char ITC(unsigned int x)
{
return (x <= 9) ? x + '0' : '?';
}
void kernel_main()
{
char out[512];
int onOut = 0;
print_clear();
print_set_color(PRINT_COLOR_GREEN, PRINT_COLOR_BLACK);
for (int i = 0; i < 100; i++) {
unsigned int len = getLen(i);
unsigned int n = i;
unsigned int offs = len;
while (n != 0) {
out[onOut + offs--] = ITC(n % 10);
n /= 10;
}
out[onOut + len + 1] = '\n';
onOut += len + 1;
}
out[onOut + 1] = 0;
for (int i = 0; out[i] != 0; i++) {
print_char(out[i]);
}
}