postfix_evaluation.c File Reference

Postfix evaluation algorithm implementation More...

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>

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Data Structures
struct	Stack
	for printf() and scanf() More...

Functions
void	push (int8_t opd)
	Function to push on the stack.
int8_t	pop ()
	Function to pop from the stack.
int8_t	evaluate (char post[])
	Function to evaluate postfix expression.
static void	test ()
	Self-test implementations.
int	main ()
	Main function.

Variables
struct Stack	st
	global declaration of stack st

Detailed Description

Postfix evaluation algorithm implementation

The input postfix expression is of type string upto 49 characters (including space delimiters). Supported operations- '+', '-', '/', '*', ''

Author

Kumar Yash

Function Documentation

evaluate()

int8_t evaluate

(

char

post[]

)

Function to evaluate postfix expression.

Parameters

post	the input postfix expression

Returns

evaluated answer

                             {
    int8_t it1;
    int8_t it2;
    int8_t temp;
    int8_t number;
    int i;
    for(i = 0; i < strlen(post); i++) {
        if(post[i] == ' ') {
            continue;           // ignore delimiter
        }
        else if(isdigit(post[i])) {
            number = 0;
            do {
                number = number * 10 + (post[i]-'0');
                i++;
            } while(i < strlen(post) && isdigit(post[i]));
            push(number);
        }
        else {
            it2 = pop();
            it1 = pop();
            switch(post[i]) {
                case '+':
                temp = it1 + it2; break;
                case '-':
                temp = it1 - it2; break;
                case '*':
                temp = it1 * it2; break;
                case '/':
                temp = it1 / it2; break;
                case '%':
                temp = it1 % it2; break;
                default:
                printf("Invalid operator"); exit(1);
            }
            push(temp);
        }
    }
    return pop();
}

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main()

int main

(

void

)

Main function.

Returns

0 on exit

initialize

run self-test implementations

           {
    st.top = -1;            /// initialize
    test();             /// run self-test implementations
    return 0;
}

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pop()

int8_t pop

(

void

)

Function to pop from the stack.

Returns

popped number

< to store the popped value to be returned

             {
    int8_t item;                ///< to store the popped value to be returned
    if(st.top == -1) {      // underflow condition
        printf("Stack underflow...");
        exit(1);
    }
    item = st.stack[st.top];
    st.top--;
    return item;
}

push()

void push

(

int8_t

opd

)

Function to push on the stack.

Parameters

opd	number to be pushed in the stack

Returns

void

                      {
    if(st.top == 19)    {       // overflow condition
        printf("Stack overflow...");
        exit(1);
    }
    st.top++;
    st.stack[st.top] = opd;
}

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test()

static void test ( void  )

static

Self-test implementations.

Returns

void

this ensures that the algorithm works as expected

this ensures that the algorithm works as expected

                   {
    /* check sample test case
       input: "2 10 + 9 6 - /"
       expected output: 4
     */
    char temp1[50] = "2 10 + 9 6 - /";
    assert(evaluate(temp1) == 4);           /// this ensures that the algorithm works as expected
    /* input: "4 2 + 3 5 1 - * +"
       expected output: 18
     */
    char temp2[50] = "4 2 + 3 5 1 - * +";
    assert(evaluate(temp2) == 18);          /// this ensures that the algorithm works as expected
    printf("All tests have successfully passed!\n");
}

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