add 6-5

Data Structures and Algorithms (English)/6-5_Evaluate Postfix Expression (25).c

@@ -0,0 +1,55 @@
+ElementType EvalPostfix(char *expr) {
+  ElementType stack[Max_Expr+10];
+  int top = -1;
+  char *p = expr;
+  char token[Max_Expr];
+
+  while (*p) {
+      int i = 0;
+      // Skip spaces
+      while (*p == ' ') p++;
+      if (!*p) break;
+
+      // Get next token
+      while (*p && *p != ' ') {
+          token[i++] = *p++;
+      }
+      token[i] = '\0';
+
+      // Process token
+      if (strlen(token) == 1 && (token[0] == '+' || token[0] == '-' || token[0] == '*' || token[0] == '/')) {
+          // Not enough operands
+          if (top < 1) return Infinity;
+
+          ElementType op2 = stack[top--];
+          ElementType op1 = stack[top--];
+
+          switch (token[0]) {
+              case '+':
+                  stack[++top] = op1 + op2;
+                  break;
+              case '-':
+                  stack[++top] = op1 - op2;
+                  break;
+              case '*':
+                  stack[++top] = op1 * op2;
+                  break;
+              case '/':
+                  // Division by zero check
+                  if (op2 == 0) return Infinity;
+                  stack[++top] = op1 / op2;
+                  break;
+          }
+      } else {
+          // Convert string to number
+          ElementType num;
+          if (sscanf(token, "%lf", &num) != 1) return Infinity;
+          stack[++top] = num;
+      }
+  }
+
+  // Final stack should have exactly one value
+  if (top != 0) return Infinity;
+
+  return stack[top];
+}