There is a task, to write calculator, which recieves strings cosisting of:

• chars '0'-'9',
• brackest '(', ')',
• chars ' ', '-', '*', '/', '^',

and performing following ops:

• addition
• substraction
• multiplication
• integer division
• power.

Arcitecture of solution should include recursive descent

My code:

#include <stdio.h>
#include <setjmp.h>

jmp_buf begin;
char curlex;

void getlex(void);
int expr(void);
int add_sub(void);
int mult_div(void);
int power(void);
void error();

int main() {
    int result;
    setjmp(begin);
    printf("==>");
    getlex();
    result=expr();
    if ( curlex != '\n') error();
    printf("\n%d\n",result);
    return 0;
}

void getlex() {
    while ( ( curlex=getchar()) == ' ');
}

void error(void) {
    printf("\nERROR!\n");
    while(getchar()!='\n');
    longjmp(begin,1);
}

int expr() {
    int e=add_sub();
    while (curlex == ' ' || curlex == '-')
        if (curlex == ' ')
        {getlex(); e =add_sub();}
        else if (curlex == '-')
        {getlex(); e-=add_sub();}
    return e;
}

int add_sub() {

    int a=mult_div();
    while (curlex == '*' || curlex == '/')
        if (curlex == '*')
        {getlex(); a*=mult_div();}
        else if (curlex == '/')
        {getlex(); a/=mult_div();}
    return a;
}

int mult_div() {
    int a=power();
    while (curlex == '^')
    {getlex(); for(int k=0;k<power(); k  , a*=power());}
    return a;
}

int power() {
    int m;
    switch(curlex){
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9': m= curlex-'0'; break;
        case '(': getlex(); m=expr();
                  if ( curlex == ')') break;
        default : error();
    }

    getlex();
    return m;
}

Code performs almost everything mentioned, except power-operation. I can't find a bug. There is also an issue with right association of power operation. That means expression 3^1^2 gives 9, but should give 3.

Please help!

CodePudding user response：

You are calling power() too often in mult_div(). Once you have a value returned by power() you should calculate the power and continue:

int mult_div() {
    int a=power();
    while (curlex == '^') 
    {
        getlex();
         a = calc_power(a, power());
    }
    return a;
}

To make it easier I used a helper function to calculate the power:

int calc_power(int a, int b)
{
    int res = 1;
    for (int i = 0; i < b; i  ) res *= a;
    return res;
}

https://godbolt.org/z/n4KhWx6j1

curlex should be an int, because that's what getchar returns: https://en.cppreference.com/w/c/io/getchar