mirror of
https://github.com/TheAlgorithms/C
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88a82991f2
* 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>
129 lines
2.9 KiB
C
129 lines
2.9 KiB
C
/**
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* @file
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* @brief [Postfix evaluation algorithm](https://www.includehelp.com/c/evaluation-of-postfix-expressions-using-stack-with-c-program.aspx) implementation
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* @details
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* The input postfix expression is of type string upto 49 characters (including space delimiters).
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* Supported operations- '+', '-', '/', '*', '%'
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* @author [Kumar Yash](https://github.com/kumaryash18)
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*/
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#include <stdio.h> /// for IO operations
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#include <string.h> /// for strlen()
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#include <ctype.h> /// for isdigit()
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#include <stdlib.h> /// for exit()
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#include <stdint.h> /// for int8_t
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#include <assert.h> /// for assert
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/**
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* @brief array implementation of stack using structure
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*/
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struct Stack {
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int8_t stack[20]; ///< array stack
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int top; ///< stores index of the top element
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};
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struct Stack st; ///< global declaration of stack st
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/**
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* @brief Function to push on the stack
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* @param opd number to be pushed in the stack
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* @returns void
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*/
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void push(int8_t opd) {
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if(st.top == 19) { // overflow condition
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printf("Stack overflow...");
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exit(1);
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}
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st.top++;
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st.stack[st.top] = opd;
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}
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/**
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* @brief Function to pop from the stack
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* @returns popped number
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*/
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int8_t pop() {
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int8_t item; ///< to store the popped value to be returned
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if(st.top == -1) { // underflow condition
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printf("Stack underflow...");
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exit(1);
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}
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item = st.stack[st.top];
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st.top--;
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return item;
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}
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/**
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* @brief Function to evaluate postfix expression
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* @param post the input postfix expression
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* @returns evaluated answer
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*/
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int8_t evaluate(char post[]) {
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int8_t it1;
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int8_t it2;
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int8_t temp;
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int8_t number;
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int i;
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for(i = 0; i < strlen(post); i++) {
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if(post[i] == ' ') {
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continue; // ignore delimiter
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}
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else if(isdigit(post[i])) {
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number = 0;
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do {
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number = number * 10 + (post[i]-'0');
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i++;
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} while(i < strlen(post) && isdigit(post[i]));
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push(number);
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}
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else {
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it2 = pop();
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it1 = pop();
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switch(post[i]) {
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case '+':
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temp = it1 + it2; break;
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case '-':
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temp = it1 - it2; break;
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case '*':
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temp = it1 * it2; break;
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case '/':
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temp = it1 / it2; break;
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case '%':
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temp = it1 % it2; break;
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default:
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printf("Invalid operator"); exit(1);
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}
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push(temp);
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}
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}
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return pop();
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}
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/**
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* @brief Self-test implementations
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* @returns void
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*/
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static void test() {
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/* check sample test case
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input: "2 10 + 9 6 - /"
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expected output: 4
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*/
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char temp1[50] = "2 10 + 9 6 - /";
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assert(evaluate(temp1) == 4); /// this ensures that the algorithm works as expected
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/* input: "4 2 + 3 5 1 - * +"
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expected output: 18
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*/
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char temp2[50] = "4 2 + 3 5 1 - * +";
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assert(evaluate(temp2) == 18); /// this ensures that the algorithm works as expected
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printf("All tests have successfully passed!\n");
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}
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/**
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* @brief Main function
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* @returns 0 on exit
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*/
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int main() {
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st.top = -1; /// initialize
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test(); /// run self-test implementations
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return 0;
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}
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