#include <string.h>
#include <stdio.h>

#include <string.h>
#include <stdio.h>
#include <assert.h>
#include <stdbool.h>

int solution(char *str) {
    static const size_t LEN = 3;
    static const char* one  = "one";
    static const char* two  = "two";
    int operand[2] = {0, 0};
    int operand_index = 0;
    char op = 0x00;

    char* ptr = str;
    while (*ptr != '\0') {
        int cmp = strncmp(ptr, one, LEN);
        if (cmp == 0) {
            operand[operand_index++] = 1;
            ptr += LEN;
        }
        cmp = strncmp(ptr, two, LEN);
        if (cmp == 0) {
            operand[operand_index++] = 2;
            ptr += LEN;
        }

        if (operand_index == 2) {
            operand_index = 0;
            int a = operand[0];
            int b = operand[1];
            int res = 0;
            if (op == '+') res = a + b;
            else res = a - b;
            operand[operand_index++] = res;
        }

        if (*ptr == '+') {
            op = '+';
        } else if (*ptr == '-') {
            op = '-';
        } else {
            assert(true && "Invalid parsing!");
        }
        ++ptr;

    }

    return operand[0];
}

int main() {
    char* str = "one+two-one-one+two+one";
    int ret = solution(str);
    printf("input: %s = %d\n", str, ret);
    return 0;
}