Initial commit

22 files changed, 994 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..9e5e780
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*a.out
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;
+	}
+}
diff --git a/one/char.c b/one/char.c
new file mode 100644
index 0000000..91cfc75
--- /dev/null
+++ b/one/char.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+
+#define IN 1 /* inside of a word */
+#define OUT 0 /* outside of a word */
+
+/* count lines, words, and characters */
+void
+wc()
+{
+	/*
+	 * c must be big enough to hold any value getchar() returns so we use
+	 * int instead of char to hold EOF, an integer defined in stdio
+	 */
+	int c, nl, nw, nc, state;
+	state = OUT;
+	nl = nw = nc = 0;
+	while ((c = getchar()) != EOF) {
+		++nc;
+		if (c == '\n') {
+			++nl;
+		}
+		/* && is higher precedence than || */
+		if (c == ' ' || c == '\t' || c == '\n') {
+			state = OUT;
+		} else if (state == OUT) {
+			state = IN;
+			++nw;
+		}
+	}
+	printf("%d %d %d\n", nl, nw, nc);
+}
+
+/* print input separated by new lines */
+void
+print_word_line()
+{
+	int c;
+	while ((c = getchar()) != EOF) {
+		if (c == ' ' || c == '\t' || c == '\n') {
+			putchar('\n');
+		} else {
+			putchar(c);
+		}
+	}
+}
+
+int
+main()
+{
+	wc();
+	/* print_word_line(); */
+	return 0;
+}
diff --git a/one/count.c b/one/count.c
new file mode 100644
index 0000000..0f5bb82
--- /dev/null
+++ b/one/count.c
@@ -0,0 +1,41 @@
+#include <stdio.h>
+
+/* count digits, white space, and others */
+int
+main()
+{
+	int c, i, nwhite, nother;
+	int ndigit[10];
+	int nchar[26];
+	nwhite = nother = 0;
+
+	for (i = 0; i < 26; ++i) {
+		if (i < 10) {
+			ndigit[i] = 0;
+		}
+		nchar[i] = 0;
+	}
+
+	while ((c = getchar()) != EOF) {
+		if (c >= '0' && c <= '9') {
+			++ndigit[c - '0'];
+		} else if (c == ' ' || c == '\t' || c == '\n') {
+			++nwhite;
+		} else if (c >= 'a' && c <= 'z') {
+			++nchar[c - 'a'];
+		} else {
+			++nother;
+		}
+	}
+
+	printf("digits =");
+	for (i = 0; i < 10; ++i) {
+		printf(" %d", ndigit[i]);
+	}
+	printf("\nchars =");
+	for (i = 0; i < 26; ++i) {
+		printf(" %d", nchar[i]);
+	}
+	printf("\nwhite space = %d\nother = %d\n", nwhite, nother);
+	return 0;
+}
diff --git a/one/longest.c b/one/longest.c
new file mode 100644
index 0000000..cf19ac9
--- /dev/null
+++ b/one/longest.c
@@ -0,0 +1,86 @@
+#include <stdio.h>
+
+#define MAXLINE 1024
+
+/*
+ * read a line into s, return length,
+ * assume length is less than MAXLINE
+ * and the line number is less than MAXLINE
+ */
+int
+get_line(char s[], int lim)
+{
+	int c, i;
+	for (i = 0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; ++i) {
+		s[i] = c;
+	}
+	if (c == '\n') {
+		/* increment i after assignment */
+		s[i++] = c;
+	}
+	/* put null character at end of string */
+	s[i] = '\0';
+	return i;
+}
+
+/* copy from into to */
+void
+copy(char to[], char from[])
+{
+	int i = 0;
+	/* '\0' marks end of string */
+	while ((to[i] = from[i]) != '\0') {
+		++i;
+	}
+}
+
+/* remove trailing whitespace */
+void
+trim(char s[], int i)
+{
+	/* skip null character and new line */
+	i -= 2;
+	while (i >= 0 && (s[i] == ' ' || s[i] == '\t')) {
+		--i;
+	}
+	s[i] = '\0';
+}
+
+/* flip characters in string */
+void
+reverse(char s[])
+{
+	int i = 0;
+	while (s[i] != '\n') {
+		++i;
+	}
+	--i;
+	char c;
+	for (int j = 0; j < i / 2; ++j) {
+		c = s[i - j];
+		s[i - j] = s[j];
+		s[j] = c;
+	}
+}
+
+/* print longest input line */
+int
+main()
+{
+	char line[MAXLINE], longest[MAXLINE];
+
+	int len;
+	int max = 0;
+	while ((len = get_line(line, MAXLINE)) > 0) {
+		if (len > max) {
+			max = len;
+			copy(longest, line);
+		}
+	}
+	if (max > 0) {
+		/* trim(longest, max); */
+		/* reverse(longest); */
+		printf("%s", longest);
+	}
+	return 0;
+}
diff --git a/one/power.c b/one/power.c
new file mode 100644
index 0000000..dd2ba2d
--- /dev/null
+++ b/one/power.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int
+power(int m, int n)
+{
+	int p;
+	for (p = 1; n > 0; --n) {
+		p *= m;
+	}
+	return p;
+}
+
+int
+main()
+{
+	int i;
+	for (i = 0; i < 10; ++i) {
+		printf("%d %d %d\n", i, power(2, i), power(-3, i));
+	}
+	return 0;
+}
diff --git a/one/tab.c b/one/tab.c
new file mode 100644
index 0000000..f9c6dc5
--- /dev/null
+++ b/one/tab.c
@@ -0,0 +1,59 @@
+#include <stdio.h>
+
+/* XXX: dependent on file size */
+#define MAX 1024
+
+void detab()
+{
+	char detab[MAX];
+
+	int c, i;
+	i = 0;
+	while (i < MAX && (c = getchar()) != EOF) {
+		if (c == '\t') {
+			for (int t = 0; t < 8; ++t) {
+				detab[i + t] = ' ';
+			}
+			i += 8;
+		} else {
+			detab[i++] = c;
+		}
+	}
+	detab[i] = '\0';
+	printf("%s", detab);
+}
+
+void entab()
+{
+	char entab[MAX];
+
+	int c, i, s;
+	i = s = 0;
+	while (i < MAX && (c = getchar()) != EOF) {
+		if (c == ' ') {
+			++s;
+		} else {
+			while (s > 0) {
+				if (s >= 8) {
+					entab[i++] = '\t';
+					s -= 8;
+				} else {
+					entab[i++] = ' ';
+					--s;
+				}
+			}
+			entab[i++] = c;
+		}
+	}
+
+	entab[i] = '\0';
+	printf("%s", entab);
+}
+
+int
+main()
+{
+	detab();
+	/* entab(); */
+	return 0;
+}
diff --git a/one/temp.c b/one/temp.c
new file mode 100644
index 0000000..54c99ba
--- /dev/null
+++ b/one/temp.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+
+#define LOWER 0
+#define UPPER 300
+#define STEP 20
+
+void
+temp()
+{
+	float fahr, cel;
+
+	printf("Fahrenheit-Celsius table\n");
+	for (fahr = UPPER; fahr >= LOWER; fahr -= STEP) {
+		cel = (5.0 / 9.0) * (fahr - 32.0);
+		/* 3 and 6 characters wide with 1 digit after the dot */
+		printf("%3.0f %6.1f\n", fahr, cel);
+	}
+
+	printf("\nCelsius-Fahrenheit table\n");
+	for (cel = LOWER; cel <= UPPER; cel += STEP) {
+		fahr = 9.0 / 5.0 * cel + 32.0;
+		printf("%3.0f %6.0f\n", cel, fahr);
+	}
+}
+
+int
+main()
+{
+	temp();
+	return 0;
+}
diff --git a/one/uncom.c b/one/uncom.c
new file mode 100644
index 0000000..455f138
--- /dev/null
+++ b/one/uncom.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+/* XXX: dependent on file size */
+#define MAX 2048
+
+int
+main()
+{
+	char uncomment[MAX];
+	int c, i;
+	i = 0;
+	while (i < MAX && (c = getchar()) != EOF) {
+		if (c == '/') {
+			c = getchar();
+			if (c == '*') {
+				while ((c = getchar()) != '/') {
+					if (c == '\n') {
+						putchar('\n');
+					} else {
+						putchar(' ');
+					}
+				}
+			} else if (c == '/') {
+				while ((c = getchar()) != '\n') {
+					putchar(' ');
+				}
+				putchar('\n');
+			}
+		} else {
+			putchar(c);
+		}
+	}
+	return 0;
+}
diff --git a/three/conv.c b/three/conv.c
new file mode 100644
index 0000000..d3e654e
--- /dev/null
+++ b/three/conv.c
@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <limits.h>
+
+void
+reverse(char s[])
+{
+	int i = 0;
+	while (s[i] != '\0') {
+		++i;
+	}
+	--i;
+	char c;
+	for (int j = 0; j < i / 2; ++j) {
+		c = s[i - j];
+		s[i - j] = s[j];
+		s[j] = c;
+	}
+}
+
+void
+itoa(int n, char s[])
+{
+	int i, sign;
+	if ((sign = n) < 0) {
+		n = -n - 1;
+	}
+	i = 0;
+	do {
+		s[i++] = n % 10 + '0';
+	} while ((n /= 10) > 0);
+	if (sign < 0) {
+		s[i++] = '-';
+	}
+	s[i] = '\0';
+	reverse(s);
+}
+
+void
+itob(int n, char s[], int b)
+{
+	int i, sign;
+	if ((sign = n) < 0) {
+		n = -n;
+	}
+	i = 0;
+	do {
+		s[i++] = (n % b <= 9) ? n % b + '0' : n % b - 10 + 'a';
+	} while ((n /= b) > 0);
+	if (sign < 0) {
+		s[i++] = '-';
+	}
+	s[i] = '\0';
+	reverse(s);
+}
+
+int
+main()
+{
+	char s[32];
+	itoa(INT_MIN, s);
+	printf("%s\n", s);
+	itob(380, s, 16);
+	printf("%s\n", s);
+	return 0;
+}
diff --git a/three/escape.c b/three/escape.c
new file mode 100644
index 0000000..1f1dfe9
--- /dev/null
+++ b/three/escape.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+
+void
+ctoe()
+{
+	int c;
+	while ((c = getchar()) != EOF) {
+		if (c == '\\') {
+			c = getchar();
+			switch(c) {
+			case 'n':
+				putchar('\n');
+				break;
+			case 't':
+				putchar('\t');
+				break;
+			default:
+				putchar(c);
+				break;
+			}
+		} else {
+			putchar(c);
+		}
+	}
+}
+
+void
+etoc()
+{
+	int c;
+	while ((c = getchar()) != EOF) {
+		switch(c) {
+		case '\n':
+			putchar('\\');
+			putchar('n');
+			break;
+		case '\t':
+			putchar('\\');
+			putchar('t');
+			break;
+		default:
+			putchar(c);
+			break;
+		}
+	}
+}
+
+int
+main()
+{
+	etoc();
+	return 0;
+}
diff --git a/three/expand.c b/three/expand.c
new file mode 100644
index 0000000..180cc98
--- /dev/null
+++ b/three/expand.c
@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int
+main()
+{
+	int c, p;
+	while ((c = getchar()) != EOF) {
+		if (c == '-') {
+			c = getchar();
+			for (++p; p < c + 1; ++p) {
+				putchar(p);
+			}
+		} else {
+			putchar(c);
+		}
+		p = c;
+	}
+	return 0;
+}
diff --git a/three/search.c b/three/search.c
new file mode 100644
index 0000000..30426c7
--- /dev/null
+++ b/three/search.c
@@ -0,0 +1,25 @@
+#include <stdio.h>
+
+int
+binsearch(int x, int v[], int n)
+{
+	int low, high, mid;
+	low = 0;
+	high = n - 1;
+	while (low <= high) {
+		mid = (low + high) / 2;
+		if (x < v[mid]) {
+			high = mid - 1;
+		} else {
+			low = mid;
+		}
+	}
+	return -1;
+}
+
+int
+main()
+{
+	binsearch();
+	return 0;
+}
diff --git a/two/bit.c b/two/bit.c
new file mode 100644
index 0000000..28f0e7d
--- /dev/null
+++ b/two/bit.c
@@ -0,0 +1,68 @@
+#include <stdio.h>
+
+void
+itob(int n)
+{
+	for (int i = 15; i >= 0; --i) {
+		int j = n >> i;
+		if (j & 1) {
+			printf("1");
+		} else {
+			printf("0");
+		}
+	}
+	printf("\n");
+}
+
+/*
+ * return x with the n bits that begin at position p inverted, leaving the other
+ * bits unchanged
+ */
+void
+invert(unsigned x, int p, int n)
+{
+	int i;
+	i = 0;
+	while (n > 0) {
+		i |= 1 << p;
+		--p;
+		--n;
+	}
+	x ^= i;
+}
+
+/*
+ * return x with the n bits that begin at position p set to the rightmost n bits
+ * of y, leaving the other bits unchanged
+ */
+void
+setbits(unsigned x, int p, int n, unsigned y)
+{
+	x = x >> (p + 1 - n) & ~(~0 << n);
+	y = y & (~0 << n) | x;
+	printf("%d %d\n", x, y);
+	itob(x);
+	itob(y);
+}
+
+/* count the number of 1-bits */
+int
+bitcount(unsigned x)
+{
+	int b = 0;
+	while (x != 0) {
+		/* deletes rightmost 1-bit in x */
+		x &= (x - 1);
+		++b;
+	}
+	return b;
+}
+
+int
+main()
+{
+	/* setbits(5, 2, 3, 16); */
+	/* invert(16, 2, 1); */
+	printf("%d\n", bitcount(4));
+	return 0;
+}
diff --git a/two/cond.c b/two/cond.c
new file mode 100644
index 0000000..5a7b88b
--- /dev/null
+++ b/two/cond.c
@@ -0,0 +1,13 @@
+#include <stdio.h>
+
+int
+main()
+{
+	char s[] = "fOobArBaz";
+	for (int i = 0; s[i] != '\0'; ++i) {
+		(s[i] >= 'A' && s[i] <= 'Z') ? printf("%c", s[i] + 32)
+			: printf("%c", s[i]);
+	}
+	printf("\n");
+	return 0;
+}
diff --git a/two/conv.c b/two/conv.c
new file mode 100644
index 0000000..7bf218a
--- /dev/null
+++ b/two/conv.c
@@ -0,0 +1,49 @@
+#include <stdio.h>
+
+int
+lower(int c)
+{
+	if (c >= 'A' && c <= 'Z') {
+		return c + 'a' - 'A';
+	} else {
+		return c;
+	}
+}
+
+int
+atoi(char s[])
+{
+	int i, n;
+
+	n = 0;
+	for (i = 0; s[i] >= '0' && s[i] <= '9'; ++i) {
+		n = 10 * n + (s[i] - '0');
+	}
+	return n;
+}
+
+/* convert string of hex digits into int digits */
+int
+htoi(char s[])
+{
+	int i, n;
+
+	n = 0;
+	for (i = 0; s[i] >= '0' && s[i] <= 'f'; ++i) {
+		if (s[i] >= '0' && s[i] <= '9') {
+			n = 16 * n + (s[i] - '0');
+		} else if (s[i] >= 'A' && s[i] <= 'F') {
+			n = 16 * n + (s[i] - 'A' + 10);
+		} else if (s[i] >= 'a' && s[i] <= 'f') {
+			n = 16 * n + (s[i] - 'a' + 10);
+		}
+	}
+	return n;
+}
+
+int
+main()
+{
+	printf("%d\n", htoi("1f"));
+	return 0;
+}
diff --git a/two/inc.c b/two/inc.c
new file mode 100644
index 0000000..220f025
--- /dev/null
+++ b/two/inc.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+
+/* remove s2 chars from s1 */
+void
+squeeze(char s1[], char s2[])
+{
+	int i, j, k, b;
+	for (i = j = 0; s1[i] != '\0'; ++i) {
+		b = 0;
+		for (k = 0; s2[k] != '\0'; ++k) {
+			if (s1[i] == s2[k]) {
+				b = 1;
+			}
+		}
+		if (b == 0) {
+			s1[j++] = s1[i];
+		}
+	}
+	s1[j] = '\0';
+}
+
+/* return first index in s1 where any char in s2 */
+int
+any(char s1[], char s2[])
+{
+	int i, j;
+	for (i = 0; s1[i] != '\0'; ++i) {
+		for (j = 0; s2[j] != '\0'; ++j) {
+			if (s1[i] == s2[j]) {
+				return i;
+			}
+		}
+	}
+	return -1;
+}
+
+int
+main()
+{
+	char s1[] = "foobar";
+	char s2[] = "a";
+	// squeeze(s1, s2);
+	printf("%d\n", any(s1, s2));
+	return 0;
+}