c - ASCII and printf -

i have little (big, dumb?) question int , chars in c. rememeber studies "chars little integers , viceversa," , that's okay me. if need use small numbers, best way use char type.

but in code this:

#include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) {   int i= atoi(argv[1]);   printf("%d -> %c\n",i,i);   return 0; } 

i can use argument every number want. 0-127 obtain expected results (the standard ascii table) bigger or negative numbers seems work...

here example:

-181 -> k -182 -> j 300 -> , 301 -> - 

why? seems me it's cycling around ascii table, don't understand how.

when pass int corresponding "%c" conversion specifier, int converted unsigned char , written.

the values pass being converted different values when outside range of unsigned (0 uchar_max). system working on has uchar_max == 255.

when converting int unsigned char:

• if value larger uchar_max, (uchar_max+1) subtracted value many times needed bring range 0 uchar_max.
• likewise, if value less zero, (uchar_max+1) added value many times needed bring range 0 uchar_max.

therefore:

(unsigned char)-181 == (-181 + (255+1)) == 75 == 'k' (unsigned char)-182 == (-182 + (255+1)) == 74 == 'j' (unsigned char)300  == (300 - (255+1))  == 44 == ',' (unsigned char)301  == (301 - (255+1))  == 45 == '-'