Initial commit

6 files changed, 331 insertions, 0 deletions

diff --git a/four/atof.c b/four/atof.c
new file mode 100644
index 0000000..86bd651
--- /dev/null
+++ b/four/atof.c
@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <math.h>
+
+#define MAXLINE 128
+
+int
+get_line(char s[], int lim)
+{
+	int c, i;
+	i = 0;
+	while (--lim > 0 && (c = getchar()) != EOF && c != '\n') {
+		s[i++] = c;
+	}
+	if (c == '\n') {
+		s[i++] = c;
+	}
+	s[i] = '\0';
+	return i;
+}
+
+/* convert string to double-precision floating point */
+double
+atof(char s[])
+{
+	double val, power;
+	int i, sign;
+	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;
+	}
+	if (s[i] == 'e' || s[i] == 'E') {
+		return sign * val / power * pow(10, s[++i] - '0');
+	}
+	return sign * val / power;
+}
+
+int
+main()
+{
+	double sum;
+	char line[MAXLINE];
+	sum = 0;
+	while (get_line(line, MAXLINE) > 0) {
+		printf("\t%g\n", sum += atof(line));
+	}
+	return 0;
+}
diff --git a/four/calc.c b/four/calc.c
new file mode 100644
index 0000000..cb484ad
--- /dev/null
+++ b/four/calc.c
@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#define MAXOP 100
+#define NUMBER '0'
+
+int getop(char[]);
+void push(double);
+double pop(void);
+double peek();
+void ungets();
+
+int
+main()
+{
+	int type, var;
+	double op1, op2, r;
+	char s[MAXOP];
+	char v[26];
+
+	/* reverse Polish calculator */
+	while ((type = getop(s)) != EOF) {
+		switch (type) {
+		case NUMBER:
+			push(atof(s));
+			break;
+		case '+':
+			push(pop() + pop());
+			break;
+		case '*':
+			push(pop() * pop());
+			break;
+		/* to guarantee the right order, the first value must be stored */
+		case '-':
+			op2 = pop();
+			push(pop() - op2);
+			break;
+		case '/':
+			op2 = pop();
+			if (op2 != 0.0) {
+				push(pop() / op2);
+			} else {
+				printf("error: zero divisor\n");
+			}
+			break;
+		case '%':
+			op2 = pop();
+			op1 = pop();
+			if (op1 >= 0.0 && op2 >= 0.0) {
+				push((int)op1 % (int)op2);
+			} else if (op1 < 0.0 || op2 < 0.0) {
+				push(0);
+			} else {
+				printf("error: zero divisor\n");
+			}
+			break;
+		/* print without popping */
+		case 'p':
+			printf("%f\n", peek());
+			break;
+		/* duplicate */
+		case 'd':
+			op2 = peek();
+			push(op2);
+			break;
+		/* swap top two elements */
+		case 's':
+			op2 = pop();
+			op1 = pop();
+			push(op2);
+			push(op1);
+			break;
+		case '=':
+			pop();
+			if (var > 'a' && var < 'z') {
+				v[var - 'a'] = pop();
+			}
+		case '\n':
+			r = pop();
+			printf("\t%.8g\n", r);
+			break;
+		case 'u':
+			ungets();
+			break;
+		default:
+			if (type == 'R') {
+				push(r);
+			} else if (type >= 'a' && type <= 'z') {
+				push(v[type - 'a']);
+			} else {
+				printf("error: unknown command %s\n", s);
+			}
+			break;
+		}
+		var = type;
+	}
+	return 0;
+}
diff --git a/four/getch.c b/four/getch.c
new file mode 100644
index 0000000..84582ce
--- /dev/null
+++ b/four/getch.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <string.h>
+
+#define BUFSIZE 101
+
+char buf[BUFSIZE];
+int bufp = 0;
+
+/*
+ * deliver the next character to be considered
+ * reading from the buffer if it contains a character
+ * and calling getchar if the buffer is empty
+ */
+int
+getch(void)
+{
+	return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+/* remember the characters put back on the input */
+void
+ungetch(int c)
+{
+	if (bufp >= BUFSIZE) {
+		printf("ungetch: too many characters\n");
+	} else {
+		buf[bufp++] = c;
+	}
+}
+
+void
+ungets(char s[])
+{
+	int l = strlen(s);
+	while (l) {
+		ungetch(s[--l]);
+	}
+}
diff --git a/four/getop.c b/four/getop.c
new file mode 100644
index 0000000..8870895
--- /dev/null
+++ b/four/getop.c
@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <ctype.h>
+
+#define NUMBER '0'
+
+int getch(void);
+void ungetch(int);
+
+/* get next operator or numeric operand */
+int
+getop(char s[])
+{
+	int i, c;
+
+	while((s[0] = c = getch()) == ' ' || c == '\t');
+	s[1] = '\0';
+	/* not a number */
+	if (!isdigit(c) && c != '.') {
+		return c;
+	}
+	i = 0;
+	/* collect integer part */
+	if (isdigit(c)) {
+		while (isdigit(s[++i] = c = getch()));
+	}
+	/* collect fraction part */
+	if (c == '.') {
+		while (isdigit(s[++i] = c = getch()));
+	}
+	s[i] = '\0';
+	if (c != EOF) {
+		ungetch(c);
+	}
+	return NUMBER;
+}
diff --git a/four/grep.c b/four/grep.c
new file mode 100644
index 0000000..7e6b4db
--- /dev/null
+++ b/four/grep.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <string.h>
+
+#define MAXLINE 1024
+
+int
+get_line(char s[], int lim)
+{
+	int c, i;
+	i = 0;
+	while (--lim > 0 && (c = getchar()) != EOF && c != '\n') {
+		s[i++] = c;
+	}
+	if (c == '\n') {
+		s[i++] = c;
+	}
+	s[i] = '\0';
+	return i;
+}
+
+int strindex(char s[], char t[])
+{
+	int i, j, k;
+	for (i = 0; s[i] != '\0'; ++i) {
+		for (j = i, k = 0; t[k] != '\0' && s[j] == t[k]; ++j, ++k);
+		if (k > 0 && t[k] == '\0') {
+			return i;
+		}
+	}
+	return -1;
+}
+
+int strrindex(char s[], char t[])
+{
+	int i, j, k;
+	for (i = strlen(s) - 1; i > 0; --i) {
+		for (j = i, k = strlen(t) - 1; k > 0 && s[j] == t[k]; --j, --k);
+		if (t[k] == t[0]) {
+			return i;
+		}
+	}
+	return -1;
+}
+
+int
+main()
+{
+	char line[MAXLINE];
+	char pattern[] = "ould";
+	int found = 0;
+	while (get_line(line, MAXLINE)) {
+		if (strrindex(line, pattern) >= 0) {
+			printf("%s", line);
+			++found;
+		}
+	}
+	return found;
+}
diff --git a/four/op.c b/four/op.c
new file mode 100644
index 0000000..f8e96ed
--- /dev/null
+++ b/four/op.c
@@ -0,0 +1,42 @@
+#include <stdio.h>
+
+#define MAXVAL 100
+#define NUMBER '0'
+
+int sp = 0;
+double val[MAXVAL];
+
+void
+push(double f)
+{
+	if (sp < MAXVAL) {
+		val[sp++] = f;
+	} else {
+		printf("error: stack full, can't push %g\n", f);
+	}
+}
+
+double
+pop(void)
+{
+	if (sp > 0) {
+		return val[--sp];
+	} else {
+		printf("error: stack empty\n");
+		return 0.0;
+	}
+}
+
+double
+peek()
+{
+	return val[sp - 1];
+}
+
+void
+clear()
+{
+	while (sp) {
+		val[sp--] = 0;
+	}
+}