/*****************************************************/ /*calculator.c */ /*calculator program, accepts input in reverse polish*/ /*notation. compile with */ /*gcc calculator.c */ /*note this is not a good way to write the program */ /*though, for a better way, see calc*.c in this dir. */ /*****************************************************/ #include#include /*for atof()*/ #define MAXOP 100 /*max size of operand or operator*/ #define NUMBER '0' /*signal that a number was found*/ int getop(char []); void push(double); double pop(void); /*reverse Polish calculator*/ 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 '/': op2 = pop(); if (op2 != 0.0) push(pop() / op2); else printf("error: zero divisor\n"); break; case '\n': printf("\t%.8g\n", pop()); break; default: printf("error: unknown command %s\n", s); break; } } return 0; } #define MAXVAL 100 /*max depth of val stack*/ int sp = 0; /*next free stack position*/ double val[MAXVAL]; /*value stack*/ /*push: push f onto value stack*/ void push(double f) { if (sp < MAXVAL) 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) return val[--sp]; else{ printf("error: stack empty\n"); return 0.0; } } #include int getch(void); void ungetch(int); /*getop: get next operator or numeric operand*/ int getop(char s[]) { int i, c; while ((s[0] = c = getch()) == ' ' || c == '\t') ; s[1] = '\0'; if (!isdigit(c) && c!= '.') return c; /*not a number*/ i=0; if (isdigit(c)) /*collect integer part*/ while (isdigit(s[++i] = 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]; /*buffer for ungetch*/ int bufp = 0; /*next free position in buf*/ int getch(void) /*get a (possibly pushed back) character*/ { return (bufp > 0) ? buf[--bufp] : getchar(); } void ungetch(int c) /*push character back on input*/ { if (bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++] = c; }