1 5dc21454 2023-07-14 jrmu /*
  2 5dc21454 2023-07-14 jrmu  * Exercise 3-5. Write the function itob(n,s,b) that converts the integer n
  3 5dc21454 2023-07-14 jrmu  * into a base b character representation in the string s. In particular,
  4 5dc21454 2023-07-14 jrmu  * itob(n,s,16) formats n tas a hexadecimal integer in s.
  5 5dc21454 2023-07-14 jrmu  */
  6 5dc21454 2023-07-14 jrmu 
  7 5dc21454 2023-07-14 jrmu #include <stdio.h>
  8 5dc21454 2023-07-14 jrmu #include <stdlib.h>
  9 5dc21454 2023-07-14 jrmu #include <limits.h>
 10 5dc21454 2023-07-14 jrmu #include <string.h>
 11 5dc21454 2023-07-14 jrmu 
 12 5dc21454 2023-07-14 jrmu int pow(int x, int n) {
 13 5dc21454 2023-07-14 jrmu 	int val;
 14 5dc21454 2023-07-14 jrmu 	for (val = 1; n > 0; n--) {
 15 5dc21454 2023-07-14 jrmu 		val *= x;
 16 5dc21454 2023-07-14 jrmu 	}
 17 5dc21454 2023-07-14 jrmu 	return val;
 18 5dc21454 2023-07-14 jrmu }
 19 5dc21454 2023-07-14 jrmu int itob(int n, char *s, int b) {
 20 5dc21454 2023-07-14 jrmu 	char *tr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 21 5dc21454 2023-07-14 jrmu 	int digits;
 22 5dc21454 2023-07-14 jrmu 	for (digits = 0; pow(b,digits) <= n; digits++)
 23 5dc21454 2023-07-14 jrmu 		;
 24 5dc21454 2023-07-14 jrmu 	for (int i = digits-1; i >= 0; i--) {
 25 5dc21454 2023-07-14 jrmu 		int times = (n/pow(b,i));
 26 5dc21454 2023-07-14 jrmu 		*s++ = *(tr + times);
 27 5dc21454 2023-07-14 jrmu 		n -= times * pow(b,i);
 28 5dc21454 2023-07-14 jrmu 	}
 29 5dc21454 2023-07-14 jrmu 	*s = '\0';
 30 5dc21454 2023-07-14 jrmu 	return 0;
 31 5dc21454 2023-07-14 jrmu }
 32 5dc21454 2023-07-14 jrmu int assert(char *expect, char *actual) {
 33 5dc21454 2023-07-14 jrmu 	printf("Expect: %s\n", expect);
 34 5dc21454 2023-07-14 jrmu 	printf("Actual: %s\n", actual);
 35 5dc21454 2023-07-14 jrmu 	return strcmp(expect, actual);
 36 5dc21454 2023-07-14 jrmu }
 37 5dc21454 2023-07-14 jrmu int main() {
 38 5dc21454 2023-07-14 jrmu 	char s[100];
 39 5dc21454 2023-07-14 jrmu 	char *t;
 40 5dc21454 2023-07-14 jrmu 	sprintf(t, "%d", pow(9,9));
 41 5dc21454 2023-07-14 jrmu 	assert("387420489", t);
 42 5dc21454 2023-07-14 jrmu 	itob(1208, s, 26);
 43 5dc21454 2023-07-14 jrmu 	assert("1KC", s);
 44 5dc21454 2023-07-14 jrmu 	itob(5763, s, 16);
 45 5dc21454 2023-07-14 jrmu 	assert("1683", s);
 46 5dc21454 2023-07-14 jrmu 	itob(194200, s, 8);
 47 5dc21454 2023-07-14 jrmu 	assert("573230", s);
 48 5dc21454 2023-07-14 jrmu 	itob(2, s, 8);
 49 5dc21454 2023-07-14 jrmu 	assert("2", s);
 50 5dc21454 2023-07-14 jrmu 	itob(8, s, 2);
 51 5dc21454 2023-07-14 jrmu 	assert("1000", s);
 52 5dc21454 2023-07-14 jrmu 	itob(93, s, 2);
 53 5dc21454 2023-07-14 jrmu 	assert("1011101", s);
 54 5dc21454 2023-07-14 jrmu 	/*
 55 5dc21454 2023-07-14 jrmu 	 * overflow issues
 56 5dc21454 2023-07-14 jrmu 	sprintf(t, "%x", INT_MAX);
 57 5dc21454 2023-07-14 jrmu 	itob(INT_MAX, s, 16);
 58 5dc21454 2023-07-14 jrmu 	assert(t, s);
 59 5dc21454 2023-07-14 jrmu 	*/
 60 5dc21454 2023-07-14 jrmu }
 61 5dc21454 2023-07-14 jrmu 
 62 5dc21454 2023-07-14 jrmu /*
 63 5dc21454 2023-07-14 jrmu  * thought process:
 64 5dc21454 2023-07-14 jrmu  * 1208/26
 65 5dc21454 2023-07-14 jrmu  * 46.46153846153846153846
 66 5dc21454 2023-07-14 jrmu  * too big, repeat division
 67 5dc21454 2023-07-14 jrmu  * 1208/26/26
 68 5dc21454 2023-07-14 jrmu  * 1.78698224852071005917
 69 5dc21454 2023-07-14 jrmu  * base 26: 0100
 70 5dc21454 2023-07-14 jrmu  * 1 + modulo
 71 5dc21454 2023-07-14 jrmu  * 26*26 = 676
 72 5dc21454 2023-07-14 jrmu  * 1208 - 676 = 532
 73 5dc21454 2023-07-14 jrmu  * 532 / 26 = 20
 74 5dc21454 2023-07-14 jrmu  * lookup 20 (char 9abcdefghijk)
 75 5dc21454 2023-07-14 jrmu  * base 26: 01k0 + modulo
 76 5dc21454 2023-07-14 jrmu  * 532 - 20*26 = 12
 77 5dc21454 2023-07-14 jrmu  * lookup 20 (char c)
 78 5dc21454 2023-07-14 jrmu  * base 26: 01kc
 79 5dc21454 2023-07-14 jrmu  * 5763/16 = 360.18
 80 5dc21454 2023-07-14 jrmu  * too big, repeat division
 81 5dc21454 2023-07-14 jrmu  * 5763/16/16 = 22.511
 82 5dc21454 2023-07-14 jrmu  * too big, repeat division
 83 5dc21454 2023-07-14 jrmu  * 5763/16/16/16 = 1.406
 84 5dc21454 2023-07-14 jrmu  * base 16: 1 + modulo
 85 5dc21454 2023-07-14 jrmu  * 5763-1*16*16*16 = 1667
 86 5dc21454 2023-07-14 jrmu  * 1667/16/16 = 6.5117
 87 5dc21454 2023-07-14 jrmu  * 1667-6*16*16 = 131
 88 5dc21454 2023-07-14 jrmu  * base 16: 16 + modulo
 89 5dc21454 2023-07-14 jrmu  * 131/16 = 8.1875
 90 5dc21454 2023-07-14 jrmu  * 131-8*16 = 3
 91 5dc21454 2023-07-14 jrmu  * base 16: 163
 92 5dc21454 2023-07-14 jrmu  * 194200/8/8/8/8/8 = 5.926
 93 5dc21454 2023-07-14 jrmu  * 194200 - 5*8^5 = 30360
 94 5dc21454 2023-07-14 jrmu  * 30360/8/8/8/8 = 7.41
 95 5dc21454 2023-07-14 jrmu  * 30360 - 7*8^4 = 1688
 96 5dc21454 2023-07-14 jrmu  * 1688/8/8/8 = 3.2968
 97 5dc21454 2023-07-14 jrmu  * 1688 - 3*8^3 = 152
 98 5dc21454 2023-07-14 jrmu  * 152/8/8 = 2.375
 99 5dc21454 2023-07-14 jrmu  * 152 - 2*8^2 = 24
100 5dc21454 2023-07-14 jrmu  * 24/8 = 3
101 5dc21454 2023-07-14 jrmu  * base 8: 573230
102 5dc21454 2023-07-14 jrmu  */
103 5dc21454 2023-07-14 jrmu 
104 5dc21454 2023-07-14 jrmu /*
105 5dc21454 2023-07-14 jrmu itob(INT_MIN, s, 2);
106 5dc21454 2023-07-14 jrmu printf("Expect: %s\n", "");
107 5dc21454 2023-07-14 jrmu printf("Actual: %s\n", s);
108 5dc21454 2023-07-14 jrmu itob(-5, s, 8);
109 5dc21454 2023-07-14 jrmu printf("Expect: %s\n", "");
110 5dc21454 2023-07-14 jrmu printf("Actual: %s\n", s);
111 5dc21454 2023-07-14 jrmu */
112 5dc21454 2023-07-14 jrmu