2.3

1 files changed, 46 insertions, 0 deletions

diff --git a/2/3.c b/2/3.c
new file mode 100644
index 0000000..d9e62e9
--- /dev/null
+++ b/2/3.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+
+#define MAXLEN 1000
+
+int htoi(char s[]);
+
+/* converts positive hex string to decimal */
+int main(int argc, char *argv[]) {
+  int i, c, d;
+  char s[MAXLEN];
+
+  for (i = 0; i < MAXLEN - 1 && (c = getchar()) != EOF && c != '\n'; i++) {
+    s[i] = c;
+  }
+  s[i] = 0;
+
+  d = htoi(s);
+  if (d < 0)
+    printf("invalid input: %s\n", s);
+  else
+    printf("decimal value: %d\n", d);
+
+  return 0;
+}
+
+int htoi(char s[]) {
+  int i, n;
+  char c;
+
+  n = 0;
+
+  for (i = 0; (c = s[i]) != 0; i++) {
+    if ((i == 0 && c == '0') || (i == 1 && (c == 'x' || c == 'X')))
+      continue;
+    else if (c >= '0' && c <= '9')
+      n = 16 * n + (c - '0');
+    else if (c >= 'A' && c <= 'F')
+      n = 16 * n + (c - 'A' + 10);
+    else if (c >= 'a' && c <= 'f')
+      n = 16 * n + (c - 'a' + 10);
+    else
+      return -1;
+  }
+
+  return n;
+}
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