finish chapter 3

chapter_3/exercise_3_04.c

@@ -0,0 +1,42 @@
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void reverse(char s[]);
+void itoa(int n, char s[]);
+
+int main()
+{
+    char s[32];
+    itoa(INT_MIN, s);
+    printf("%s\n", s);
+    itoa(72, s);
+    printf("%s\n", s);
+
+    return 0;
+}
+
+void reverse(char s[])
+{
+    int c;
+    for (int i = 0, j = strlen(s) - 1; i < j; ++i, --j) {
+        c = s[i], s[i] = s[j], s[j] = c;
+    }
+}
+
+void itoa(int n, char s[])
+{
+    int sign = n;
+    int i = 0;
+    // at least one character must be installed in the array
+    do {
+        s[i++] = abs(n % 10) + '0';
+    } while ((n /= 10) != 0);
+
+    if (sign < 0)
+        s[i++] = '-';
+
+    s[i] = '\0';
+    reverse(s);
+}

chapter_3/exercise_3_05.c

@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+char int2char(int n);
+void itob(int n, char s[], int b);
+void reverse(char s[]);
+
+int main()
+{
+    int x = 255;
+    char s[32];
+    itob(x, s, 16);
+    printf("%s", s);
+
+    return 0;
+}
+
+void reverse(char s[])
+{
+    int c;
+    for (int i = 0, j = strlen(s) - 1; i < j; ++i, --j) {
+        c = s[i], s[i] = s[j], s[j] = c;
+    }
+}
+
+void itob(int n, char s[], int b)
+{
+    if (b < 2 || b > 36) {
+        fprintf(stderr, "unsupported base %d", b);
+        exit(1);
+    }
+
+    int sign = n;
+    int i = 0;
+    // at least one character must be installed in the array
+    do {
+        s[i++] = int2char(abs(n % b));
+    } while ((n /= b) != 0);
+
+    if (sign < 0)
+        s[i++] = '-';
+
+    s[i] = '\0';
+    reverse(s);
+}
+
+char int2char(int n)
+{
+    if (0 <= n && n <= 9) return n + '0';
+    return 'A' + n - 10;
+}

chapter_3/exercise_3_06.c

@@ -0,0 +1,46 @@
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void reverse(char s[]);
+void itoa(int n, char s[], int minwidth);
+
+int main()
+{
+    char s[32];
+    itoa(INT_MIN, s, 12);
+    printf("%s\n", s);
+    itoa(72, s, 12);
+    printf("%s\n", s);
+
+    return 0;
+}
+
+void reverse(char s[])
+{
+    int c;
+    for (int i = 0, j = strlen(s) - 1; i < j; ++i, --j) {
+        c = s[i], s[i] = s[j], s[j] = c;
+    }
+}
+
+void itoa(int n, char s[], int minwidth)
+{
+    int sign = n;
+    int i = 0;
+    // at least one character must be installed in the array
+    do {
+        s[i++] = abs(n % 10) + '0';
+    } while ((n /= 10) != 0);
+
+    if (sign < 0)
+        s[i++] = '-';
+
+    while (i < minwidth) {
+        s[i++] = ' ';
+    }
+
+    s[i] = '\0';
+    reverse(s);
+}