4.2

1 files changed, 48 insertions, 0 deletions

diff --git a/4/2.c b/4/2.c
new file mode 100644
index 0000000..0f842e8
--- /dev/null
+++ b/4/2.c
@@ -0,0 +1,48 @@
+#include <ctype.h>
+#include <stdio.h>
+
+#define MAXLEN 1000
+
+/* converts string to numeric representation of doubles */
+double atof(char s[]);
+
+int main(int argc, char *argv[]) {
+  int i, c;
+  char s[MAXLEN];
+
+  printf("input: ");
+
+  for (i = 0; i < MAXLEN - 1 && (c = getchar()) != '\n' && c != EOF; i++)
+    s[i] = c;
+  s[i] = 0;
+
+  printf("numeric: %f\n", atof(s));
+
+  return 0;
+}
+
+double atof(char s[]) {
+  int i, sign;
+  double val, power;
+
+  for (i = 0; isspace(s[i]); i++)
+    ;
+
+  sign = (s[i] == '-') ? -1 : 1;
+
+  if (s[i] == '+' || s[i] == '-')
+    i++;
+
+  for (val = 0.0; isdigit(s[i]); i++)
+    val = 10.0 * val + (s[i] - '0');
+
+  if (s[i] == '.')
+    i++;
+
+  for (power = 1.0; isdigit(s[i]); i++) {
+    val = 10.0 * val + (s[i] - '0');
+    power *= 10.0;
+  }
+
+  return sign * val / power;
+}
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