#include <stdio.h> #include <ctype.h> #include <string.h> #define MAX 100 // Maximum size of stack // Global stack and top index int stack[MAX]; int top = -1; // Function to push an integer onto the stack void push(int x) { // Push (Inserting Element in stack) operation if (top == MAX - 1) { printf("Stack overflow\n"); } else { stack[++top] = x; // Push the integer onto the stack } } // Function to pop an integer from the stack int pop() { // Pop (Removing element from stack) if (top == -1) { // Check if stack is empty printf("Stack underflow\n"); return -1; // Return -1 to indicate underflow } else { return stack[top--]; // Return the top integer and remove it } } // Function to perform the operation int performOperation(int operand1, int operand2, char operation) { switch (operation) { case '+': return operand1 + operand2; case '-': return operand1 - operand2; case '*': return operand1 * operand2; case '/': return operand1 / operand2; default: return 0; // Return 0 for unknown operation } } // Function to evaluate the postfix expression int evaluatePostfixExpression(char* expression) { int length = strlen(expression); // Iterate from left to right for (int i = 0; i < length; i++) { char c = expression[i]; if (isdigit(c)) { // Convert char digit to int and push onto the stack push(c - '0'); // Push the integer value of the digit } else { // Pop the top two elements for the operation int operand2 = pop(); // Order of popping is important for correct operation int operand1 = pop(); // Perform the operation and push the result back onto the stack int result = performOperation(operand1, operand2, c); push(result); } } return pop(); // Return the final result } int main() { char expression[MAX]; printf("Enter a postfix expression: "); scanf("%s", expression); int result = evaluatePostfixExpression(expression); printf("Result of Postfix Expression: %d\n", result); return 0; }
Method 2
#include <stdio.h>
#include <ctype.h> // for isdigit function
#define MAX 100 // Stack size
// Stack structure
struct Stack {
int data[MAX];
int top;
};
// Function to initialize the stack
void initializeStack(struct Stack* stack)
{
stack->top = -1;
}
// Function to push an element onto the stack
void push(struct Stack* stack, int value) {
if (stack->top < MAX - 1) {
stack->top++;
stack->data[stack->top] = value;
} else {
printf("Stack overflow\n");
}
}
// Function to pop an element from the stack
int pop(struct Stack* stack) {
if (stack->top >= 0) {
int value = stack->data[stack->top];
stack->top--;
return value;
} else {
printf("Stack underflow\n");
return -1;
}
}
// Function to perform the operation
int performOperation(int operand1, int operand2, char operation) {
switch (operation) {
case '+':
return operand1 + operand2;
case '-':
return operand1 - operand2;
case '*':
return operand1 * operand2;
case '/':
return operand1 / operand2;
default:
return 0;
}
}
// Function to evaluate the postfix expression
int evaluatePostfixExpression(char* expression) {
struct Stack stack;
initializeStack(&stack);
for (int i = 0; expression[i] != '\0'; i++) {
char c = expression[i];
if (isdigit(c)) {
// Convert char digit to int and push onto the stack
push(&stack, c - '0');
} else {
// Pop the top two elements for the operation
int operand2 = pop(&stack);
int operand1 = pop(&stack);
// Perform the operation and push the result back onto the stack
int result = performOperation(operand1, operand2, c);
push(&stack, result);
}
}
// The final result should be the only item left in the stack
return pop(&stack);
}
int main() {
char expression[MAX];
// user for input
printf("Enter a postfix expression: ");
scanf("%s", expression);
int result = evaluatePostfixExpression(expression);
printf("Result of Postfix Expression: %d\n", result);
return 0;
}
