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DS/C/Lab/Week6/InfixToPrefix.c

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+#include <stdio.h>
+#include <string.h>
+
+#define MAX_SIZE 100
+
+char stack[MAX_SIZE];
+int top = -1;
+
+void push(char item) {
+    if (top >= MAX_SIZE - 1) {
+        printf("Stack Overflow\n");
+        return;
+    }
+    stack[++top] = item;
+}
+
+char pop() {
+    if (top < 0) {
+        printf("Stack Underflow\n");
+        return -1;
+    }
+    return stack[top--];
+}
+
+int precedence(char symbol) {
+    switch (symbol) {
+        case '^': return 3;
+        case '*':
+        case '/': return 2;
+        case '+':
+        case '-': return 1;
+        default: return 0;
+    }
+}
+
+void reverse(char *str) {
+    int len = strlen(str);
+    int i, j;
+    char temp;
+    for (i = 0, j = len - 1; i < j; i++, j--) {
+        temp = str[i];
+        str[i] = str[j];
+        str[j] = temp;
+    }
+}
+
+int isalnum(char c) {
+    return ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'));
+}
+
+void infixToPrefix(char infix[], char prefix[]) {
+    char symbol, temp[2];
+    int i, j = 0;
+    
+    reverse(infix);
+    
+    for (i = 0; infix[i] != '\0'; i++) {
+        symbol = infix[i];
+        if (isalnum(symbol)) {
+            prefix[j++] = symbol;
+        } else if (symbol == ')') {
+            push(symbol);
+        } else if (symbol == '(') {
+            while ((temp[0] = pop()) != ')') {
+                prefix[j++] = temp[0];
+            }
+        } else {
+            while (top > -1 && precedence(stack[top]) > precedence(symbol)) {
+                prefix[j++] = pop();
+            }
+            push(symbol);
+        }
+    }
+    
+    while (top > -1) {
+        prefix[j++] = pop();
+    }
+    prefix[j] = '\0';
+    
+    reverse(prefix);
+}
+
+int main() {
+    char infix[MAX_SIZE], prefix[MAX_SIZE];
+    printf("Enter infix expression: ");
+    fgets(infix, MAX_SIZE, stdin);
+    infix[strcspn(infix, "\n")] = 0;  // Remove newline if present
+    infixToPrefix(infix, prefix);
+    printf("Prefix expression: %s\n", prefix);
+    return 0;
+}