SimpleCalc

#include <stdio.h>

#define STACKSIZE 100
#define MAXLEN 1000

double stack[STACKSIZE];
int top;

void push(double f);
double pop(void);
double atof(char s[]);
int getline(char line[]);
int isNum(char c);
void convert(char s[], char t[], const int len);

int main(void) {
    char number[MAXLEN];
    int len = 0;
    double num = 0.0;
    char line[MAXLEN], result[MAXLEN];
    while ((len = getline(line)) != 0) {
        int t1 = 0, t2 = 0;
        for (int i = 0; i < len; ++i) {
            if (line[i] == '(') ++t1;
            else if (line[i] == ')') ++t2;
        }
        if (t1 != t2) { printf("Mismatched parenthesis!\n"); continue; }
        convert(line, result, len);
        printf("%s\n", result);
        len = 0;
        for (int i = 0; result[i] != '\0'; ++i) {
            switch (result[i]) {
                case '+':
                    num = pop();
                    push(pop() + num);
                    ++i;
                    break;
                case '-':
                    num = pop();
                    push(pop() - num);
                    ++i;
                    break;
                case '*':
                    num = pop();
                    push(pop() * num);
                    ++i;
                    break;
                case '/':
                    num = pop();
                    push(pop() / num);
                    ++i;
                    break;
                case ' ':
                    number[len] = '\0';
                    push(atof(number));
                    len = 0;
                    break;
                default:
                    number[len++] = result[i];
                    break;
            }
        }
        printf("%f\n\n", pop());
        top = 0;
    }
    return 0;
}

void push(double f) {
    stack[top++] = f;
}

double pop(void) {
    return stack[--top];
}

double atof(char s[]) {
    int sign = 1, value = 0, power = 1 , i = 0;
    if (s[i] == '-') { sign = -1; ++i; }
    for (; isNum(s[i]); ++i) value = 10 * value + (s[i] - '0');
    if (s[i] == '.') ++i;
    while (isNum(s[i])) {
        value = 10 * value + (s[i++] - '0');
        power *= 10;
    }
    return sign * value/(double)power;
}

int getline(char line[]) {
    int c;
    int i = 0;
    while ((c = getchar()) != '\n') {
        line[i++] = c;
    }
    line[i] = '\0';
    return i;
}

int isNum(char c) {
    return ((c >= '0' && c <= '9')) ? 1 : 0;
}

void convert(char s[], char t[], const int len) {
    int k = 0, l = 0;
    char stack[MAXLEN];
    for (int i = 0; i < len; ++i) {
        if (isNum(s[i])  || s[i] == '.') { t[k++] = s[i]; if((i+1 != len) && !(isNum(s[i+1]) || s[i+1] == '.')) t[k++] = ' '; }
        else if (s[i] == ')') {
            while (stack[--l] != '(') {
                t[k++] = stack[l];
                t[k++] = ' ';
            }
            --l;
        }
        else {
            switch(s[i]) {
                case '(':
                    stack[l++] = '(';
                    break;
                case '+':
                case '-':
                    while (stack[--l] != '(' && l>=0) {
                        t[k++] = stack[l];
                        t[k++] = ' ';
                    }
                    stack[++l] = s[i];
                    break;
                case '*':
                case '/':
                    while (stack[--l] != '+' && stack[l] != '-' && stack[l] != '(' && l>=0) {
                        t[k++] = stack[l];
                        t[k++] = ' ';
                    }
                    stack[++l] = s[i];
                    break;
                default:
                    break;
            }
            if (s[i] != ' ') stack[l++] = s[i];
        }
    }
    if (t[k-1] != ' ') t[k++] = ' ';
    while (l > 0) {  t[k++] = stack[--l]; t[k++] = ' '; }
    t[k] = '\0';
}