The C Programming Language, 2nd Edition, by Kernighan and Ritchie
Exercise 4.05 on page 79
Add access to library functions like sin , exp , and pow . See <math.h> in Appendix B, Section 4.
Solution by Bob Wightman
#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 /* The new additions deal with adding functions from math.h to the calculator. In anticipation of the following exercise the code deals with an identifier in the following manner: If the identifier is recognised as one of the supported mathematical functions then that function from the library is called. If the identifier is not one of the supported functions, even if it is a valid function from math.h it is ignored. The main changes are the introduction of another define value (IDENTIFIER) along with its associated case in the switch statement. Getop has also been changed to deal with reading in alphabetical characters. This is exercise 4-5 from Kernighan & Ritchie, page 79. */ int Getop(char s[]); void push(double val); double pop(void); void showTop(void); void duplicate(void); void swapItems(void); void clearStack(); void dealWithName(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: dealWithName(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("\n\t%.8g\n", pop()); break; default: printf("\nError: unknown command %s.\n", s); break; } } return EXIT_SUCCESS; } #define MAXVAL 100 int sp = 0; /* Next free stack position. */ double val[MAXVAL]; /* value stack. */ /* push: push f onto stack. */ void push(double f) { if(sp < MAXVAL) val[sp++] = f; else printf("\nError: stack full can't push %g\n", f); } /*pop: pop and return top value from stack.*/ double pop(void) { if(sp > 0) return val[--sp]; else { printf("\nError: stack empty\n"); return 0.0; } } void showTop(void) { if(sp > 0) printf("Top of stack contains: %8g\n", val[sp-1]); else printf("The stack is empty!\n"); } /* Alternatively: void showTop(void) { double item = pop(); printf("Top of stack contains: %8g\n", item); push(item); } */ 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; } /* deal with a string/name this may be either a maths function or for future exercises: a variable */ void dealWithName(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 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; /*size_t len;*/ /* Skip whitespace */ while((s[0] = c = getch()) == ' ' || c == '\t') ; s[1] = '\0'; if(isalpha(c)) { i = 0; while(isalpha(s[i++] = c )) c = getch(); s[i - 1] = '\0'; if(c != EOF) unGetch(c); return IDENTIFIER; } /* Not a number but may contain a unary minus. */ if(!isdigit(c) && c != '.' && c != '-') return c; if(c == '-') { next = getch(); if(!isdigit(next) && next != '.') { return c; } c = next; } else c = getch(); while(isdigit(s[++i] = c)) c = getch(); if(c == '.') /* Collect fraction part. */ while(isdigit(s[++i] = c = getch())) ; s[i] = '\0'; if(c != EOF) unGetch(c); return NUMBER; } #define BUFSIZE 100 char buf[BUFSIZE]; int bufp = 0; /* Getch: get a ( possibly pushed back) character. */ int getch(void) { return (bufp > 0) ? buf[--bufp]: getchar(); } /* unGetch: push character back on input. */ void unGetch(int c) { if(bufp >= BUFSIZE) printf("\nUnGetch: too many characters\n"); else buf[bufp++] = c; }
Solution by menonsahab
/* The previous solution while using the mathematical functions, does not check whether there are sufficient number of elements in the stack to perform that particular operation. I've made the necessary changes. */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> #include <math.h> #define MAXOP 100 #define NUMBER 0 #define MAXVAL 100 #define BUFSIZE 100 #define IDENTIFIER 1 int getop(char *); void push(double); double pop(void); int getch(void); void ungetch(int); void viewstack(void); void showTop(void); void swap(void); void duplicate(void); void clearStack(void); void mathfunc(char *); int bufp = 0; char buf[BUFSIZE]; 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"); exit(1); //return 0.0; } } int getch(void) { return (bufp > 0) ? buf[--bufp] : getchar(); } void ungetch(int c) { if(bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++] = c; } int getop(char *s) { int i, c, d, flag; while((s[0] = c = getch()) == ' ' || c == '\t'); s[1] = '\0'; if(!isalnum(c) && c != '.' && c != '-') return c; if(c == '-') { d = getch(); if(d == ' ') return c; else ungetch(d); } i = 0; if(isalnum(c) || c == '-') while(isalnum(s[++i] = c = getch())); if(c == '.') while(isalnum(s[++i] = c = getch())); s[i] = '\0'; if(c != EOF) ungetch(c); flag = 1; for(i = 0; s[i] != '\0'; i++) if(!isalpha(s[i])) { flag = 0; break; } if(flag == 1) return IDENTIFIER; else return NUMBER; } void viewstack(void) { int i; printf("\nstack:\n"); for(i = sp - 1; i >= 0; i--) printf("%lf\n", val[i]); } void showTop(void) { sp > 0 ? printf("\t%.8g\n", val[sp-1]) : printf("stack is empty\n"); } void swap(void) { double temp; if(sp < 1) printf("error: stack has less than 2 elements, can't swap\n"); else { temp = val[sp - 1]; val[sp - 1] = val[sp - 2]; val[sp - 2] = temp; } } void duplicate(void) { if(sp > MAXVAL - 1) printf("error: stack is full, can't duplicate\n"); else { double temp = pop(); push(temp); push(temp); ++sp; } } void clearStack(void) { sp = 0; } void mathfunc(char *s) { if(strcmp(s, "sin") == 0) { if(sp < 1) printf("error: stack is empty, can't use sin function\n"); else push(sin(pop())); } else if(strcmp(s, "cos") == 0) { if(sp < 1) printf("error: stack is empty, can't use cos function\n"); else push(cos(pop())); } else if(strcmp(s, "exp") == 0) { if(sp < 1) printf("error: stack is empty, can't use exp function\n"); else push(exp(pop())); } else if(strcmp(s, "pow") == 0) { if(sp < 2) printf("error: stack has less than 2 elements, can't use pow function\n"); else { double op2; op2 = pop(); push(pow(pop(), op2)); } } else printf("%s is not a supported function\n", s); } int main() { int type; double op2; char s[MAXOP]; while((type = getop(s)) != EOF) { //viewstack(); // Use this function if you wish to see the stack after every iteration switch(type) { case NUMBER: push(atof(s)); break; case IDENTIFIER: mathfunc(s); break; case '+': push(pop() + pop()); break; case '*': push(pop() * pop()); break; 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(); if(op2 != 0.0) push(fmod(pop(), op2)); else printf("error: division by zero\n"); break; case '?': // show top item on stack without popping showTop(); break; case '~': // swap top two elements of the stack swap(); break; case '#': // duplicate the top element duplicate(); break; case '!': // clearStack clearStack(); break; case '\n': printf("\t%.8g\n", pop()); break; default: printf("error: unknown command %s\n", s); break; } //viewstack(); } return 0; }
Solution by Luke Panayi
#include <stdio.h> #include <stdlib.h> #include <ctype.h> #include <math.h> #include <string.h> #define MAXOP 100 #define NUMBER '0' #define MAXVAL 100 #define BUFSIZE 100 int getop(char []); void push(double); double pop(void); int getch(void); void ungetch(int); 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; } } void peek(void) { if (sp > 0) { printf("%g\n", val[sp]); } else { printf("error: stack empty\n"); } } void swap(void) { if (sp > 1) { double tmp; tmp = val[sp]; val[sp] = val[sp-1]; val[sp-1] = tmp; } else { printf("error: not enough elements in stack\n"); } } void clear(void) { sp = 0; //should be enough to simply set the pointer to 0, old values will be overwritten. } void duplicate(void) { if (sp < MAXVAL -1) { push(val[sp]); } else { printf("error: stack full\n"); } } int getop(char s[]) { int i, c, j; while ((s[0] = c = getch()) == ' ' || c == '\t'); s[1] = '\0'; if (!isdigit(c) && !isalpha(c) && c != '.' && c != '-') return c; i = 0; if (c == '-') { s[i] = c; if (!isdigit(c = getch())) { return '-'; } else s[++i] = c; } if (isalpha(c)) { j = 0; char t[4]; while (isalpha(t[++j] = c = getch())); t[j] = '\0'; if (strcmp(t, "sin")) //we could had done all the math.h functions but effort return 's'; if (strcmp(t, "cos")) return 'c'; if (strcmp(t, "tan")) return 't'; if (strcmp(t, "e")) return 'e'; printf("error: unsupported function or malformed input\n"); return '\n'; } if (isdigit(c)) while (isdigit(s[++i] = c = getch())); if (c == '.') while (isdigit(s[++i] = c = getch())); s[i] = '\0'; if (c != EOF) ungetch(c); return NUMBER; } char buf[BUFSIZE]; int bufp = 0; int getch(void) { return (bufp > 0) ? buf[--bufp] : getchar(); } void ungetch(int c) { if (bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++] = c; } int main() { int type; double op2; char s[MAXOP]; while ((type = getop(s)) != EOF) { switch (type) { case NUMBER: push(atof(s)); break; case '+': push(pop() + pop()); break; case '*': push(pop() * pop()); break; case '-': op2 = pop(); push(pop() - op2); break; case '/': if (op2 != 0.0) { op2 = pop(); push(pop() / op2); } else printf("error: zero divisor\n"); break; case '%': op2 = pop(); if (op2 != 0.0) { push(fmod(pop(), op2)); } else printf("error: zero divisor\n"); break; case '^': op2 = pop(); push(pow(pop(), op2)); break; case 's': push(sin(pop())); break; case 'c': push(cos(pop())); break; case 't': push(tan(pop())); break; case 'e': push(exp(pop())); break; case '\n': printf("\t%.8g\n", pop()); break; } } return 0; }
Solution by anonymous
I opted to go the simple route of adding commands to access library functions by mapping them to special characters. They are all added to the select statement in main. Also, since the code is rather simple, I didn't write separate functions for them.
#include <stdio.h> #include <stdlib.h> // for atof() #include <ctype.h> #include <math.h> /* Exercise 4-5. Add access to library functions like sin, exp, and pow. See <math.h> in Appendix B, Section 4. */ #define MAXOP 100 // max size of operand or operator #define NUMBER '0' // signal that a number was found #define MAXVAL 100 // maximum depth of val stack #define BUFSIZE 100 enum boolean {FALSE, TRUE}; int sp = 0; // next free stack position double val[MAXVAL]; // value stack char buf[BUFSIZE]; // buffer for ungetch int bufp = 0; // next free position in buf int getop(char s[]); void push(double f); double pop(void); int getch(void); void ungetch(int c); void printTop(void); void duplicateTop(void); void swapTopTwo(void); // reverse Polish calculator // note: convert ((((-1 - 2) * (4 + -5)) / -3) % 5) * (-1 - -10) to -1 2 - 4 -5 + * -3 / 5 % -1 -10 - * for reverse Polish notation. -1 2 - 4 -5 + * -3 / 5 % -1 -10 - * == -9 int main() { int type; double op2; char s[MAXOP]; char skipNextNewline = FALSE; while ((type = getop(s)) != EOF) { switch (type) { case NUMBER: push(atof(s)); // convert the string to type double and push it on the stack break; case '+': push(pop() + pop()); // pop last two digits to sum them and push the result on the stack break; case '*': push(pop() * pop()); // pop last two digits to multiply them and push the result on the stack break; case '-': /* Because + and * are commutative operators, the order in which the popped operands are combined is irrelevant, but for - and / the left and right operands must be distinguished. In push(pop() - pop());, the order in which the two calls of pop are evaluated is not defined. To guarantee the right order, it is necessary to pop the first value into a temporary variable. Hence op2 = pop() in - and / but not in + and * */ op2 = pop(); push(pop() - op2); // pop last two digits to subtract them in the correct order and push the result on the stack break; case '/': op2 = pop(); if (op2 != 0.0) push(pop() / op2); // pop last two digits to divide them in the correct order and push the result on the stack else printf("error: zero divisor\n"); break; case '%': op2 = pop(); if (op2 != 0.0) push(fmod(pop(), op2)); // pop last two digits in the correct order to find the modulus and push the result on the stack else printf("error: zero divisor\n"); break; case '?': printTop(); skipNextNewline = TRUE; break; case '#': duplicateTop(); skipNextNewline = TRUE; break; case '~': swapTopTwo(); skipNextNewline = TRUE; break; case '!': // sets next free stack position to zero (meaning the value stack is empty). // all of the original values are still there, but they will no longer be accessible by the current functions and they will be overwritten when new elements are stored sp = 0; skipNextNewline = TRUE; break; case '$': push(sin(pop())); skipNextNewline = TRUE; break; case '@': push(exp(pop())); skipNextNewline = TRUE; break; case '^': op2 = pop(); push(pow(pop(), op2)); // pop last two digits in the correct order to raise a number to the given power skipNextNewline = TRUE; break; case '&': push(sqrt(pop())); skipNextNewline = TRUE; break; case ',': push(fabs(pop())); skipNextNewline = TRUE; break; case '\n': if (skipNextNewline) skipNextNewline = FALSE; else printf("\t%.8g\n", pop()); // get the final result break; default: printf("error: unknown command %s\n", s); break; } } return 0; } // push: push f onto value stack void push(double f) { if (sp < MAXVAL) // if value stack still has space, add f val[sp++] = f; else printf("error: stack full, can't push %g\n", f); } // pop: pop and return top value from stack double pop(void) { if (sp > 0) // if the next free stack position is greater than zero, return the highest level item from stack return val[--sp]; else { printf("error: stack empty\n"); return 0.0; } } // getop: get next operator or numeric operand int getop(char s[]) { int i, c; while ((s[0] = c = getch()) == ' ' || c == '\t') // skip white space ; s[1] = '\0'; // terminate string in case input is not a number (s is expected to be a string throughout program) if (!isdigit(c) && c != '.' && c != '-') return c; // not a number. Probably an operator, so return it. Minus operator is a special case and is handled right before return NUMBER; i = 0; if (c == '-' || isdigit(c)) // collect integer(s), if any, after first digit found or after minus symbol found while (isdigit(s[++i] = c = getch())) ; if (c == '.') // collect fraction part if period is found while (isdigit(s[++i] = c = getch())) ; s[i] = '\0'; // terminate string after digits were captured if (c != EOF) ungetch(c); // since we read to far, push the last read char back on the getch buffer. This buffer is read first before getting the next char from input if (i == 1 && s[0] == '-') // if s[0] == '-' && s[1] == '\0', return minus operator return '-'; return NUMBER; } // get a (possibly pushed back) character // checks to see if there are any chars in buffer. If there are, get those and return it. If not, call getchar() from stdio.h to get next char from input int getch(void) { return (bufp > 0) ? buf[--bufp] : getchar(); } // push character back on input // if bufp is less than BUFSIZE, there is room to store more chars to be read by getch next and it stores c and updates the index for it void ungetch(int c) { if (bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++] = c; } // prints the top element in the value stack void printTop(void) { if (sp > 0) printf("\t%.8g\n", val[sp - 1]); else printf("error: stack empty\n"); } void duplicateTop(void) { if (sp < MAXVAL) // only need to see if there is space for one more push(val[sp - 1]); // duplicates top item else printf("error: stack full, can't duplicate top element\n"); } void swapTopTwo(void) { // if sp == 2, there are at least two elements stored if (sp > 1) { // <third> <second> <first> double first = pop(); // <third> <second> double second = pop(); // <third> push(first); // <third> <first> push(second); // <third> <first> <second> } else printf("error: can't swap top two, not enough elements\n"); }
