C Exercises: Check a parentheses string is balanced or not using stack

Last update on August 04 2025 13:04:36 (UTC/GMT +8 hours)

7. Balanced Parentheses and Delimiters

Write a C program that checks whether a string of parentheses is balanced or not using stack.

An opening symbol that has a corresponding closing symbol is considered balanced parentheses, where the parentheses are correctly nested and the opening and closing symbols are the same.

Valid balanced parentheses:
• [ [ { { ( ( ) ) } } ] ]
• [ ] [ ] [ ] ( ) { }

Invalid balanced parentheses:
• ( [ ) ]
• ( ( ( ) ] ) )
• [ { ( ) ]

Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_SIZE 100

// Global variables for stack and top
char stack[MAX_SIZE];
int top = -1;

// Function to push a character onto the stack
void push(char data) {
    if (top == MAX_SIZE - 1) {
        printf("Overflow stack!\n");
        return;
    }
    top++;
    stack[top] = data;
}

// Function to pop a character from the stack
char pop() {
    if (top == -1) {
        printf("Empty stack!\n");
        return ' ';
    }
    char data = stack[top];
    top--;
    return data;
}

// Function to check if two characters form a matching pair of parentheses
int is_matching_pair(char char1, char char2) {
    if (char1 == '(' && char2 == ')') {
        return 1;
    } else if (char1 == '[' && char2 == ']') {
        return 1;
    } else if (char1 == '{' && char2 == '}') {
        return 1;
    } else {
        return 0;
    }
}

// Function to check if the expression is balanced
int isBalanced(char* text) {
    int i;
    for (i = 0; i < strlen(text); i++) {
        if (text[i] == '(' || text[i] == '[' || text[i] == '{') {
            push(text[i]);
        } else if (text[i] == ')' || text[i] == ']' || text[i] == '}') {
            if (top == -1) {
                return 0; // If no opening bracket is present
            } else if (!is_matching_pair(pop(), text[i])) {
                return 0; // If closing bracket doesn't match the last opening bracket
            }
        }
    }
    if (top == -1) {
        return 1; // If the stack is empty, the expression is balanced
    } else {
        return 0; // If the stack is not empty, the expression is not balanced
    }
}

// Main function
int main() {
   char text[MAX_SIZE];
   printf("Input an expression in parentheses: ");
   scanf("%s", text);

   // Check if the expression is balanced or not
   if (isBalanced(text)) {
       printf("The expression is balanced.\n");
   } else {
       printf("The expression is not balanced.\n");
   }
   return 0;
}

Output:

Input an expression in parentheses: {[])
The expression is not balanced.
 -----------------------------------------
 Input an expression in parentheses: ((()))
The expression is balanced.
 -----------------------------------------
 Input an expression in parentheses: ())
The expression is not balanced.
 -----------------------------------------
 Input an text of parentheses: ([]){}[[(){}]{}]
The expression is balanced.
 -----------------------------------------
 Input an expression in parentheses: [(]))
The expression is not balanced.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to check if an expression containing curly braces, square brackets, and parentheses is balanced.
• Write a C program to validate /XML tag pairs using stack operations.
• Write a C program to check for balanced parentheses and indicate the position of the first mismatch.
• Write a C program to support custom delimiter pairs and verify if a given expression is balanced using a stack.

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