K and R C, Solution to Exercise 4-5:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Write a C program to access to library functions like sin, exp, and pow. See “math.h” for more details.Read more about C Programming Language .

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#include<stdlib.h>
#include<stdio.h>
#include<ctype.h>
#include<math.h>
#include <string.h>

#define MAXOP 100
#define NUMBER       0
#define IDENTIFIER   1
#define TRUE 1
#define FALSE 0



int Getop(char s[]);
void push(double val);
double pop(void);
void showTop(void);
void duplicate(void);
void swapItems(void);
void clearStack();
void mathfnc(char s[]);

int main(void)
{
 int type;
 double op2;
 char s[MAXOP];
 int flag = TRUE;

 while((type = Getop(s)) != EOF)
 {
  switch(type)
  {
  case NUMBER:
   push(atof(s));
   break;
  case IDENTIFIER:
   mathfnc(s);
   break;
  case '+':
  push(pop() + pop());
  break;
  case '*':
   push(pop() * pop());
   break;
  case '-':
   op2 = pop();
   push(pop()- op2);
   break;
  case '/':
   op2 = pop();
   if(op2)
    push(pop() / op2);
   else
    printf("nError: division by zero!");
   break;
  case '%':
   op2 = pop();
   if(op2)
    push(fmod(pop(), op2));
   else
    printf("nError: division by zero!");
   break;
  case '?':
   showTop();
   break;
  case '#':
   duplicate();
   break;
  case '~':
   swapItems();
   break;
  case '!':
   clearStack();
  case 'n':
   printf("nt%.8gn", pop());
   break;
  default:
   printf("nError: unknown command %s.n", s);
   break;
  }
 }
 return EXIT_SUCCESS;
}

#define MAXVAL 100

int sp = 0;         
double val[MAXVAL]; 

/* push: push f onto stack. */
void push(double f)
{
 if(sp < MAXVAL)
  val[sp++] = f;
 else
  printf("nError: stack full can't push %gn", f);
}

/*pop: pop and return top value from stack.*/
double pop(void)
{
 if(sp > 0)
  return val[--sp];
 else
 {
  printf("nError: stack emptyn");
  return 0.0;
 }
}

void showTop(void)
{
 if(sp > 0)
  printf("Top of stack contains: %8gn", val[sp-1]);
 else
  printf("The stack is empty!n");
}



void duplicate(void)
{
 double temp = pop();

 push(temp);
 push(temp);
}

void swapItems(void)
{
 double item1 = pop();
 double item2 = pop();

 push(item1);
 push(item2);
}

void clearStack(void)
{
 sp = 0;
}

/*check string s for supported math functions */
void mathfnc(char s[])
{
 double op2;

 if( 0 == strcmp(s, "sin"))
  push(sin(pop()));
 else if( 0 == strcmp(s, "cos"))
  push(cos(pop()));
 else if (0 == strcmp(s, "exp"))
  push(exp(pop()));
 else if(!strcmp(s, "pow"))
 {
  op2 = pop();
  push(pow(pop(), op2));
 }
 else
  printf("%s Error: is not a supported function.n", s);
}

int getch(void);
void unGetch(int);

/* Getop: get next operator or numeric operand. */
int Getop(char s[])
{
 int i = 0;
 int c;
 int next;


 /* Skip whitespace */
 while((s[0] = c = getch()) == ' ' || c == 't')
  ;
 s[1] = '