Thread: Failing to Use Recursion - Arithmetic Calculator

Hi all!

My most recent programming woes stem from a lack of reading comprehension on my part. I am supposed to code a simple arithmetic calculator to handle +/- expressions of any length,

i.e. 2 + 3 - -7 + 9

To avoid making my post overly-long with code, here's the link to my previous iteration of program (non-recursive, using a switch): Coursework/evaluate.c at master * burgerkong/Coursework * GitHub

Unfortunately, I failed to realize that I need to use recursion in my implementation of the program; and the below version (my current attempt) has not been working:

Code:

#include <stdio.h>#include <stdlib.h>


float s_exp(float sub_exp, char op);
char get_op();
float get_num();


int main()
{
    float exp;
    char op;
    printf("Please enter an arithmetic expression: ");
    exp = get_num();
    op = get_op();
    printf("%f", s_exp(exp, op));
    return 0;
}


float s_exp(float sub_exp, char op)
{
    if(op != '\n')
    {
        switch(op)
        {
        case '+':
            sub_exp = sub_exp + get_num();
            break;
        case '-':
            sub_exp = sub_exp - get_num();
            break;
        case ' ':
            break;
        default:
            printf("Sorry, there was an invalid operator in your equation.  Please only use +/-.");
            exit(0);
        }
        get_op();
        s_exp(sub_exp, op);
    }
    return sub_exp;
}


char get_op()
{
    char next_op;
    next_op = getchar();
    return next_op;
}


float get_num()
{
    float next_num;
    scanf("%f", &next_num);
    return next_num;
}

Currently, entering an expression causes an infinite loop. Entering a single integer works correctly.

How should I implement recursion? And why does my program not correctly interpret the operator?

Thanks, and sorry if I'm missing something obvious (I feel like I am, but have been struggling for the past hour).

Hey Salem!

Thanks for the tip, definitely a brainfart on my end with regards to the recursion implementation.

Code:

#include <stdio.h>#include <stdlib.h>


float s_exp(float sub_exp, char op);
char get_op();
float get_num();


int main()
{
    float exp;
    char op;
    printf("Please enter an arithmetic expression: ");
    exp = get_num();
    op = get_op();
    printf("Result: %.2f", s_exp(exp, op));
    return 0;
}


float s_exp(float sub_exp, char op)
{
    if(op != '\n')
    {
        switch(op)
        {
        case '+':
            sub_exp = sub_exp + get_num();
            break;
        case '-':
            sub_exp = sub_exp - get_num();
            break;
        case ' ':
            break;
        default:
            printf("Sorry, there was an invalid operator in your equation.  Please only use +/- when using this program in the future.");
            exit(0);
        }
        op = get_op();
        sub_exp = s_exp(sub_exp, op);
    }
    return sub_exp;
}


char get_op()
{
    char next_op;
    next_op = getchar();
    return next_op;
}


float get_num()
{
    float next_num;
    scanf("%f", &next_num);
    return next_num;
}

Here's where my program currently sits. Have to run some test cases, but it seems to be functioning! Thanks <3