A Example for DLLs

DynamicLinkLibrary/my_str-dll/my_str.c

@@ -0,0 +1,110 @@
+#include "my_str.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <string.h>
+
+/*
+  Use this command to run
+
+  gcc -DMY_STR_BUILD_DLL -shared my_str.c -o my_str.dll -Wl,--out-implib,libmy_str.a
+
+*/
+
+
+// Define maximum capacity for stacks
+#define MAX 100
+
+// Operand stack to store numbers
+static double numStack[MAX];
+static int numTop = -1;
+
+// Operator stack to store characters (+, -, *, /, ()
+static char opStack[MAX];
+static int opTop = -1;
+
+// Stack operations
+static void pushNum(double val) { numStack[++numTop] = val; }
+static double popNum() { return numStack[numTop--]; }
+static void pushOp(char op) { opStack[++opTop] = op; }
+static char popOp() { return opStack[opTop--]; }
+static char peekOp() { return opStack[opTop]; }
+
+// Returns priority of operators: Higher value means higher precedence
+static int priority(char op) {
+    if (op == '+' || op == '-') return 1;
+    if (op == '*' || op == '/') return 2;
+    return 0; // Parentheses have the lowest priority inside the stack
+}
+
+// Performs arithmetic operations
+static double applyOp(double a, double b, char op) {
+    switch (op) {
+        case '+': return a + b;
+        case '-': return a - b;
+        case '*': return a * b;
+        case '/': 
+            if (b == 0) {
+                printf("Error: Division by zero\n");
+                return 0;
+            }
+            return a / b;
+    }
+    return 0;
+}
+
+// Main function to evaluate infix expression
+double evaluate(const char* exp) {
+    for (int i = 0; exp[i] != '\0'; i++) {
+        // 1. Skip whitespace characters
+        if (exp[i] == ' ' || exp[i] == '\t') continue;
+
+        // 2. If the character is a digit, parse the full number (supports multi-digit)
+        if (isdigit(exp[i])) {
+            double val = 0;
+            while (i < strlen(exp) && isdigit(exp[i])) {
+                val = (val * 10) + (exp[i] - '0');
+                i++;
+            }
+            pushNum(val);
+            i--; // Decrement index because the loop increments it
+        } 
+        // 3. If left parenthesis, push it to the operator stack
+        else if (exp[i] == '(') {
+            pushOp(exp[i]);
+        } 
+        // 4. If right parenthesis, solve the entire bracket
+        else if (exp[i] == ')') {
+            while (opTop != -1 && peekOp() != '(') {
+                double val2 = popNum();
+                double val1 = popNum();
+                char op = popOp();
+                pushNum(applyOp(val1, val2, op));
+            }
+            if (opTop != -1) popOp(); // Remove '(' from stack
+        } 
+        // 5. If character is an operator
+        else {
+            // While the top of the stack has same or higher precedence, calculate
+            while (opTop != -1 && priority(peekOp()) >= priority(exp[i])) {
+                double val2 = popNum();
+                double val1 = popNum();
+                char op = popOp();
+                pushNum(applyOp(val1, val2, op));
+            }
+            // Push current operator to stack
+            pushOp(exp[i]);
+        }
+    }
+
+    // 6. Entire expression parsed, calculate remaining operations in stack
+    while (opTop != -1) {
+        double val2 = popNum();
+        double val1 = popNum();
+        char op = popOp();
+        pushNum(applyOp(val1, val2, op));
+    }
+
+    // The final result is the only element left in the operand stack
+    return popNum();
+}