9.1.c

#include <stdio.h>
double min(double, double);
int main(void) {
	double x, y;

	printf("Enter two numbers (q to quit): ");
	while (scanf("%lf %lf", &x, &y) == 2) {
		printf("The smaller number is %f.\n", min(x,y));
		printf("Next two values (q to quit): ");
	}
	printf("Bye!\n");

	return 0;
}
double min(double a, double b) {
	return a < b ? a : b;
}
/*
double min(double a, double b)
{
 if (a < b)
 return a;
 else
 return b;
}
*/

9.2.c

#include <stdio.h>
void chline(char ch, int i, int j);
int main(void) {
	char ch;
	int col, row;

	printf("Enter a character (# to quit): ");
	while ( (ch = getchar()) != '#') {
		if (ch == '\n')
			continue;
		printf("Enter number of columns and number of rows: ");
		if (scanf("%d %d", &col, &row) != 2)
			break;
		chline(ch, col, row);
		printf("\nEnter next character (# to quit): ");
	}
	printf("Bye!\n");

	return 0;
}
// start rows and cols at 0
void chline(char ch, int i, int j) {
	int col, row;
	for (row = 0; row < j ; row++) {
		for (col = 0; col < i; col++)
			putchar(ch);
		putchar('\n');
	}
	
	return;
}

9.3.c

#include <stdio.h>
void chline(char ch, int i, int j);
int main(void) {
	char ch;
	int col, row;

	printf("Enter a character (# to quit): ");
	while ( (ch = getchar()) != '#') {
		if (ch == '\n')
			continue;
		printf("Enter number of columns and number of rows: ");
		if (scanf("%d %d", &col, &row) != 2)
			break;
		chline(ch, col, row);
		printf("\nEnter next character (# to quit): ");
	}
	printf("Bye!\n");

	return 0;
}
// start rows and cols at 0
void chline(char ch, int i, int j) {
	int col, row;
	for (row = 0; row < j ; row++) {
		for (col = 0; col < i; col++)
			putchar(ch);
		putchar('\n');
	}
	
	return;
}

9.4.c

#include <stdio.h>
double average(double num1, double num2);

int main(void) {
	double num1, num2, result;
	double rnum1, rnum2, rresult;
	
	printf("Enter two numbers (q to quit):\n");
	while(scanf("%lf %lf", &num1, &num2) == 2) {
		rnum1 = 1 / num1;
		rnum2 = 1 / num2;
		rresult = average(rnum1, rnum2);
		result = 1 / rresult;
		printf("result is %lf", result);
	}
	printf("Done.\n");
	
	return 0;
}

double average(double num1, double num2) {
	double _average = (num1 + num2) / 2;
	
	return _average;
}

9.5.c

#include <stdio.h>
void larger_of(double *p1, double *p2);
int main(void) {
	double x, y;

	printf("Enter two numbers (q to quit): ");
	while (scanf("%lf %lf", &x, &y) == 2) {
		larger_of(&x, &y);
		printf("The modified values are %f and %f.\n", x, y);
		printf("Next two values (q to quit): ");
	}
	printf("Bye!\n");

	return 0;
}
void larger_of(double *p1, double *p2) {
	if (*p1 > *p2)
		*p2 = *p1;
	else
		*p1 = *p2;
}
// alternatively:
/*
void larger_of(double *p1, double *p2)
{
 *p1= *p2 =  *p1 > *p2 ? *p1 : *p2;
}
*/

9.6.c

#include <stdio.h>
void compare(double * i, double * j, double * k);

int main(void) {
	double min, mid, max;

	printf("Enter three numbers (q to quit):\n");
	while(scanf("%lf %lf %lf", &max, &mid, &min) == 3) {
		compare(&min, &mid, &max);
		printf("%lf < %lf < %lf", min, mid, max);
	}
	printf("Done.\n");
	
	return 0;
}

void compare(double * i, double * j, double * k) {
	double n;
	if(*i > *k) {
		n = *k;
		*k = *i;
		*i = n;
	}
	if(*j > *k) {
		n = *k;
		*k = *j;
		*j = n;
	}
	if(*i > *j) {
		n = *j;
		*j = *i;
		*i = n;
	}

	return;
}

9.7.c

#include <stdio.h>
#include <ctype.h>
int position(int ch);

int main(void) {
	int ch, i;
	
	printf("Enter a charater (EOF to quit):\n");
	while((ch = getchar()) != EOF) {
		if(ch == '\n')
			continue;
		printf("%c %s letter.\n", ch, isalpha(ch) ? "is" : "isn't");
		if(isalpha(ch)) {
			i = position(ch);
			printf("%c is %d in alphabet.\n", ch, i);
		}
	}
	printf("Done.\n");
	
	return 0;
}

int position(int ch) {
	ch = tolower(ch);
	return (ch - 'a' + 1);
}

9.8.c

#include <stdio.h>
double power(double a, int b);

int main(void) {
	double x, xpow;
	int n;
	printf("Enter a number and the integer power");
	printf(" to which\nthe number will be raised. Enter q");
	printf(" to quit.\n");
	while (scanf("%lf%d", &x, &n) == 2) {
		xpow = power(x,n);
		printf("%.3g to the power %d is %.5g\n", x, n, xpow);
		printf("Enter next pair of numbers or q to quit.\n");
	}
	printf("Hope you enjoyed this power trip -- bye!\n");
	return 0;
}
double power(double a, int b) {
	double pow = 1;
	int i;

	if (b == 0) {
		if (a == 0)
			printf("0 to the 0 undefined; using 1 as the value\n");
		pow = 1.0;
	} else if (a == 0)
		pow = 0.0;
	else if (b > 0)
		for(i = 1; i <= b; i++)
			pow *= a;
	else
		pow = 1.0 / power(a, - b);
	return pow;
}

9.9.c

#include <stdio.h>
double power(double a, int b);

int main(void) {
	double x, pow;
	int n;
	printf("Enter a number and the integer power");
	printf(" to which\nthe number will be raised. Enter q");
	printf(" to quit.\n");
	while (scanf("%lf%d", &x, &n) == 2) {
		if (n == 0) {
			if (x == 0)
				printf("0 to the 0 undefined; using 1 as the value\n");
			pow = 1.0;
		} else if (x == 0)
			pow = 0.0;
		else if (n > 0)
			pow = power(x, n);
		else
			pow = 1.0 / power(x, -n);
		printf("%.3g to the power %d is %.5g\n", x, n, pow);
		printf("Enter next pair of numbers or q to quit.\n");
	}
	printf("Hope you enjoyed this power trip -- bye!\n");
	return 0;
}
double power(double a, int b) {
	if(b > 0)
		return a * power(a,b-1);
	return 1;
}

9.10.c

#include <stdio.h>
void to_base_n(int x, int base);
int main(void) {
	int number;
	int b;
	int count;

	printf("Enter an integer (q to quit):\n");
	while (scanf("%d", &number) == 1) {
		printf("Enter number base (2-10): ");
		while ((count = scanf("%d", &b))== 1
		        && (b < 2 || b > 10)) {
			printf("base should be in the range 2-10: ");
		}
		if (count != 1)
			break;
		printf("Base %d equivalent: ", b);
		to_base_n(number, b);
		putchar('\n');
		printf("Enter an integer (q to quit):\n");
	}
	printf("Done.\n");
	return 0;
}
void to_base_n(int x, int base) {
	int r;
	r = x % base;
	if (x >= base)
		to_base_n(x / base, base);
	putchar('0' + r);
	return;
}

9.11.c

#include <stdio.h>
void Fibonacci(int n);

int main(void) {
	int n;
	
	printf("Enter an integer(>0) (q to quit):\n");
	while(scanf("%d", &n) == 1 && n > 0) {
		Fibonacci(n);
		printf("Enter another one(>0) (q to quit):\n");
	}
	printf("Done.\n");
	
	return 0;
}
void Fibonacci(int n) {
	int x, y, z, i;
	x = y = 1;
	
	for(i = 1; i <= n; i++) {
		if(i <= 2)
			printf("1\n");
		else {
			z = x + y;
			x = y;
			y = z;
			printf("%d\n", z);
		}
	}
	return;
}