c - Converting char integer representations to binary -

i have char array composed of elements 5 3. array used represent number 53. should approach convert number of 3 chars binary equivalent? implementing in c, later on need rewritten in assembly. solution seek should purely low stuff work without helper libraries.

i stuck idea convert separately 5 , 4 (via mapping 5 , 4 ascii equivalents). yet idea not work sure. have idea convert char '5' int 5 right shifting byte 4. same 4. multiply 5 10 , add 4, , use division 2 algorithm find remainder , compose binary number.

in c:

int ascitointeger(char *c) {     int result = 0;     while (*c)     {         result *= 10;         result += (*c - '0');         c++;     }     return result; } 

assumes input valid.

you can head start on assembly language version compiling switches output ... assembly language! example in gnu c: gcc -s -c ascii2int.c.