Thread: C help with this reverse Polish Notation algorithm

some sums are going wrong like 321--
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Code:

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#define limit 10


int main() {
    const char cont[100];
    char temp[1], temp2[2];
    float pilha_numeros[limit], pilha_numeros_final[limit], result;
       int i, a = 0, what_byte, other_byte;
    bool check = false;
    float pilha_numero_int[100];


    printf("INSERT: ");
    scanf("%s", &cont);


    for(i = 0; i < strlen(cont); i++) {


        if(isdigit(cont[i])) {
            //printf("now : %f\n", cont[i]);
            pilha_numeros[a] = cont[i];
            temp2[0] = pilha_numeros[a];
            pilha_numero_int[a] = atof(temp2);
            printf("%d= %f\n", (i+1),pilha_numero_int[a]);
            a++;
        } else {
            what_byte = i - a +1;
            if(check) {
                other_byte = 0;
            } else {
                 other_byte = what_byte - 1;
            }
            switch(cont[i]) {
                case('+'):
                    //printf("\n        first = %f[%f] | second = %f", pilha_numero_int[qual_byte], qual_byte, pilha_numero_int[other_byte]);
                    if(check) {
                        result = pilha_numero_int[what_byte] + pilha_numeros_final[other_byte];
                    } else {
                        result = pilha_numero_int[what_byte] + pilha_numero_int[other_byte];
                    }
                    pilha_numeros_final[0] = result;
                    //printf("\ntemp result = %f", result);


                break;
                case('-'):
                    if(check) {
                        result = pilha_numero_int[what_byte] - pilha_numeros_final[other_byte];
                    } else {
                        result= pilha_numero_int[what_byte] - pilha_numero_int[other_byte];
                    }
                    pilha_numeros_final[0] = result;
                break;
                case('*'):
                    if(check) {
                        result = pilha_numero_int[what_byte] * pilha_numeros_final[other_byte];
                    } else {
                        result = pilha_numero_int[what_byte] * pilha_numero_int[other_byte];
                    }
                    pilha_numeros_final[0] = result;
                break;
                case('/'):
                    if(check) {
                        result = pilha_numero_int[what_byte] / pilha_numeros_final[other_byte];
                    } else {
                        result = pilha_numero_int[what_byte] / pilha_numero_int[other_byte];
                    }
                    pilha_numeros_final[0] = result;
                break;
            }
            check = true;
        }
    }


    printf("\n\nResult = %f\n", pilha_numeros_final[0]);
}

> const char cont[100];
Why is this const?

> char temp[1], temp2[2];
Temp1 is never used, and temp2 has no obvious \0 marking the end of the string, which will make your atof return garbage.

All your check, whatbyte and otherbyte are unnecessary.
RPN is a stack with only two operators push and pop.

Each number pushes onto the stack.
Each operator pops two numbers and pushes the result.

Push is simply
stack[pos++] = value;

Pop is
value = stack[--pos];