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feat: add postfix evaluation algorithm (#890)
* add infix to postfix converter algorithm * docs: documentation changes * docs: documentation changes * updating DIRECTORY.md * docs: documentation changes * fix: continuous integration * [test, docs]: add test case, documentation changes * docs: documentation changes * fix: continuous integration * docs: documentation changes * docs: documentation changes * test: add new test * feat: add postfix evaluation algorithm * updating DIRECTORY.md * fix: increase stack size * fix: change data type * add: parse feature * fix: CodeQL * docs: documentation changes * remove unnecessary code Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
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/** | ||
* @file | ||
* @brief [Postfix evaluation algorithm](https://www.includehelp.com/c/evaluation-of-postfix-expressions-using-stack-with-c-program.aspx) implementation | ||
* @details | ||
* The input postfix expression is of type string upto 49 characters (including space delimiters). | ||
* Supported operations- '+', '-', '/', '*', '%' | ||
* @author [Kumar Yash](https://github.com/kumaryash18) | ||
*/ | ||
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#include <stdio.h> /// for IO operations | ||
#include <string.h> /// for strlen() | ||
#include <ctype.h> /// for isdigit() | ||
#include <stdlib.h> /// for exit() | ||
#include <stdint.h> /// for int8_t | ||
#include <assert.h> /// for assert | ||
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/** | ||
* @brief array implementation of stack using structure | ||
*/ | ||
struct Stack { | ||
int8_t stack[20]; ///< array stack | ||
int top; ///< stores index of the top element | ||
}; | ||
struct Stack st; ///< global declaration of stack st | ||
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/** | ||
* @brief Function to push on the stack | ||
* @param opd number to be pushed in the stack | ||
* @returns void | ||
*/ | ||
void push(int8_t opd) { | ||
if(st.top == 19) { // overflow condition | ||
printf("Stack overflow..."); | ||
exit(1); | ||
} | ||
st.top++; | ||
st.stack[st.top] = opd; | ||
} | ||
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/** | ||
* @brief Function to pop from the stack | ||
* @returns popped number | ||
*/ | ||
int8_t pop() { | ||
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; | ||
} | ||
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/** | ||
* @brief Function to evaluate postfix expression | ||
* @param post the input postfix expression | ||
* @returns evaluated answer | ||
*/ | ||
int8_t evaluate(char post[]) { | ||
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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/** | ||
* @brief Self-test implementations | ||
* @returns void | ||
*/ | ||
static void test() { | ||
/* 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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/** | ||
* @brief Main function | ||
* @returns 0 on exit | ||
*/ | ||
int main() { | ||
st.top = -1; /// initialize | ||
test(); /// run self-test implementations | ||
return 0; | ||
} |