solutions to 04-01 and 04-02

k&r/04-funcs-and-prog-struct/04-01.c

@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <string.h>
+
+#define STRING "test string with lost of stuff"
+
+int strindex(char source[], char searchfor[]);
+
+/* pass optional searchfor arg to strindex with STRING, pretty print result */
+int main(int argc, char *argv[])
+{
+    char s[] = STRING; 
+    char *t = (argc > 1) ? argv[1] : "est";
+    
+    int i = strindex(s, t);
+    if (i < 0) {
+        printf("no match\n");
+        return 1;
+    }
+
+    printf("%s\n", s);
+    while (i--)
+        putchar(' ');
+    printf("^\n");
+    return 0;
+}
+
+/* strindex: return index of the righmost occurence of t in s, -1 if none */
+int strindex(char s[], char t[])
+{
+    int i, j;
+    const int tlen = strlen(t);
+
+    j = tlen - 1;
+    for (i = strlen(s)-1; i; i--)
+        if (s[i] != t[j])
+            j = tlen - 1;
+        else if (!(j--)) // match found
+            return i;
+    return -1;
+}

k&r/04-funcs-and-prog-struct/04-02.c

@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <math.h>
+
+#define DEC_SEP X('.') X(',')
+#define EXP_SEP X('e') X('E')
+
+double atof(char *s);
+
+int main(int argc, char *argv[])
+{
+    if (argc < 2) {
+        printf("error: expected argument\n");
+        return 1;
+    }
+    printf("%f\n", atof(argv[1]));
+    return 0;
+}
+
+
+/* macros for atof */
+#define SIGN(s) \
+    ((*s == '-') ? (s++, -1) : ((*s == '+') ? (s++, 1) : 1))
+#define ATOI(s, x, ...) \
+    for (; isdigit(*s); s++, ##__VA_ARGS__) \
+        x = 10 * x + (*s - '0')
+
+/* atof: convert string s to double */
+double atof(char s[])
+{
+    double val;
+
+    while (isspace(*s))
+        s++;
+
+    /* integer part */
+    int sign = SIGN(s);    
+    ATOI(s, val);
+
+#define X(sep) *s != sep && 
+    if (DEC_SEP 1) return sign * val;
+#undef X
+    s++;
+    /* fractional part */
+    int exp = 0; 
+    ATOI(s, val, exp--);
+    val *= sign * pow(10, exp);
+
+#define X(sep) *s != sep && 
+    if (EXP_SEP 1) return val;
+#undef X
+    s++;
+    /* exponent */
+    sign = SIGN(s);
+    exp = 0;
+    ATOI(s, exp);
+
+    return val * pow(10, sign * exp);
+}