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‎chapter-4-functions-and-program-structure/4.reverse-polish-calculator.c

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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h> // for atof()
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#include <math.h> // for fmod()
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#include "calc.h"
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#define MAXOP 100 // max size of operand or operator
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#define MAX_VAR_LEN 26 // max size of array for variables
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void mathfunc(char[]);
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void setVar(double, double);
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void getVar(char[]);
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double variables[MAX_VAR_LEN];
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int variableFlags[MAX_VAR_LEN]; // if [0] is 0, means 'a' not set, if [0] is 1, means 'a' set
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// compile with stack.c, getop.c, getch.c
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main()
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{
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int type;
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double op2;
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char s[MAXOP];
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int i;
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for (i = 0; i < MAX_VAR_LEN; i++)
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variableFlags[i] = 0;
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while ((type = getop(s)) != EOF) {
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switch(type) {
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case NUMBER:
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push(atof(s));
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break;
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case VAR:
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getVar(s);
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break;
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case FUNC:
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mathfunc(s);
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break;
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case '+':
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push(pop() + pop());
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break;
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case '*':
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push(pop() * pop());
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break;
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case '-':
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op2 = pop();
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push(pop() - op2);
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break;
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case '/':
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op2 = pop();
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if (op2 != 0.0)
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push(pop() / op2);
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else
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printf("error: zero divisor\n");
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break;
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case '%':
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op2 = pop();
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if (op2 == 0.0)
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printf("error: can not mod 0\n");
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else
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push(fmod(pop(), op2));
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break;
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case '=':
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op2 = pop();
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setVar(pop(), op2);
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break;
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case '\n':
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printf("\t%.8g\n", pop());
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break;
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default:
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printf("error: unknown command %s\n", s);
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break;
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}
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}
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return 0;
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}
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void mathfunc(char s[])
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{
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int index;
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if (0 == strrindex(s, "sin")) {
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push(sin(pop()));
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return;
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}
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if (0 == strrindex(s, "exp")) {
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push(exp(pop()));
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return;
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}
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if (0 == strrindex(s, "pow")) {
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double ey = pop();
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push(pow(pop(), ey));
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return;
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}
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printf("error: unknown func %s\n", s);
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return;
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}
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void setVar(double varIndex, double value)
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{
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int index = (int)varIndex;
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if (index < 0 || index > MAX_VAR_LEN) {
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printf("error: cannot set variable, invalid variable: %c\n", index + 'a');
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return;
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}
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variables[index] = value;
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variableFlags[index] = 1;
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push(value); // to show result
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return;
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}
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void getVar(char s[])
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{
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if (strlen(s) != 1 && s[0] != 0) {
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// if variable is 'a', s[0] == 0, strlen(s) == 0
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printf("error: cannot get variable, invalid variable: %s\n", s);
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return;
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}
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double value = atof(s);
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int index = (int)value;
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if (variableFlags[index] == 0)
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push(value);
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else
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push(variables[index]);
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return;
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}

‎chapter-4-functions-and-program-structure/calc.h

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#define NUMBER '0' // signal that a number was found
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#define FUNC '1' // signal that math function was found
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#define VAR '2' // signal that variable was found
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void push(double);
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double pop(void);
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int getop(char []);
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int getch(void);
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void ungetch(int);

‎chapter-4-functions-and-program-structure/getch.c

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#include <stdio.h>
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#include <string.h>
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#define BUFSIZE 100
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int buf[BUFSIZE];
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int bufp = 0;
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int value = EOF;
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int getch(void)
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{
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return (bufp > 0) ? buf[--bufp] : getchar();
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}
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void ungetch(int c)
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{
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if (bufp >= BUFSIZE)
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printf("ungetch: too many characters\n");
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else
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buf[bufp++] = c;
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}
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void ungetchs(char s[])
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{
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int len = strlen(s);
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while (len > 0) {
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ungetch(s[--len]);
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}
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}
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int getchOne(void)
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{
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if (value != EOF) {
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int temp = value;
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value = EOF;
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return temp;
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}
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else
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return getchar();
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}
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void ungetchOne(int c)
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{
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if (value != EOF)
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printf("ungetchOne: cannot ungetch more char\n");
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else
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value = c;
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}

‎chapter-4-functions-and-program-structure/getop.c

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#include <ctype.h>
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#include <stdio.h>
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#include <string.h>
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#include "calc.h"
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int strrindex(char source[], char searchfor[]);
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int getop(char s[])
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{
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int i, c;
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while ((s[0] = c = getch()) == ' ' || c == '\t')
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;
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s[1] = '\0';
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i = 0;
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if (c == '+' || c == '-') {
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int op = c;
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c = getch();
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if (!isdigit(c) && c != '.') {
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ungetch(c);
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return op;
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} else {
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ungetch(c);
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}
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} else if (isalpha(c)) {
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while (isalpha(s[++i] = c = getch()))
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;
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ungetch(c);
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if (i == 1) {
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s[0] = tolower(s[0]) - 'a';
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s[1] = '\0';
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return VAR;
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}
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s[++i] = '\0';
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int index;
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index = strrindex(s, "sin");
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if (index == 0)
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return FUNC;
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index = strrindex(s, "exp");
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if (index == 0)
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return FUNC;
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index = strrindex(s, "pow");
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if (index == 0)
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return FUNC;
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return 0;
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} else if (!isdigit(c) && c != '.') {
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return c;
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}
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i = 0;
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if (isdigit(c))
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while (isdigit(s[++i] = c = getch()))
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;
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if (c == '.')
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while (isdigit(s[++i] = c = getch()))
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;
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s[i] = '\0';
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if (c != EOF)
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ungetch(c);
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return NUMBER;
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}
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int strrindex(char s[], char t[])
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{
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int i, j, k;
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for (i = strlen(s) - 2; i > 0; i--) {
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for (j = i, k = strlen(t) - 1; j > 0 && k > 0 && s[j] == t[k]; j--, k--)
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;
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if (k == 0)
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return j;
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}
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return -1;
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}

‎chapter-4-functions-and-program-structure/stack.c

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#include <stdio.h>
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#define MAXVAL 100
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int sp = 0;
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double val[MAXVAL];
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void push(double f)
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{
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if (sp < MAXVAL)
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val[sp++] = f;
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else
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printf("error: stack full, can't push %g\n", f);
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}
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double pop(void)
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{
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if (sp > 0)
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return val[--sp];
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else {
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printf("error: stack empty\n");
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return 0.0;
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}
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}
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void top(void)
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{
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if (sp > 0)
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printf("stack top: %g\n", val[sp-1]);
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else
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printf("stack empty\n");
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}
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void duplicate(void)
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{
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if (sp > MAXVAL -1)
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printf("error: stack full, can't duplicate\n");
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else {
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double element = pop();
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push(element);
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push(element);
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}
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}
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void swap(void)
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{
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if (sp < 2)
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printf("error: stack size < 2, can't swap\n");
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else {
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double e1 = pop();
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double e2 = pop();
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push(e1);
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push(e2);
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}
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}
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void empty(void)
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{
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sp = 0;
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}

‎chapter-4-functions-and-program-structure/test.c

+12
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#include <stdio.h>
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#include <string.h>
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main()
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{
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char s[100];
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s[0] = 'a' - 'a';
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s[1] = 'b';
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s[2] = '\0';
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printf("strlen(s): %d\n", strlen(s));
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return 0;
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}

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