htoi

ch2/main.c

@@ -0,0 +1,49 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <assert.h>
+
+int pow_16(int exponent) {
+  return (int) pow(16.0, (double) exponent);
+}
+
+// convert hex given in string form to int
+int htoi(char *s) {
+  // may be some other nifty way where we utilize casting and type conversion
+
+  int r = 0;
+  int len = strlen(s);
+  for (int i = len - 1; i >= 0; i--) {
+    if (s[i] == 'x' || s[i] == 'X') {
+      break;
+    }
+
+    int place = len - i - 1;
+    if (s[i] >= '0' && s[i] <= '9') {
+      r = r + pow_16(place) * (s[i] - '0');
+    } else if (s[i] >= 'A' && s[i] <= 'F') {
+      r = r + pow_16(place) * (s[i] - 'A' + 10);
+    } else if (s[i] >= 'a' && s[i] <= 'f') {
+      r = r + pow_16(place) * (s[i] - 'a' + 10);
+    } else {
+      printf("WARN: not a valid hex digit: %c", s[i]);
+    }
+  }
+
+  return r;
+}
+
+int main(int argc, char **argv) {
+  printf("chapter 2\n");
+
+  char *t1 = "0x11";
+  char *t2 = "0xff";
+  char *t3 = "0xFF";
+  
+  int r = htoi(t1);
+  assert(r == 17);
+  r = htoi(t2);
+  assert(r == 255);
+  r = htoi(t3);
+  assert(r == 255);
+}