hackerrank Stacks: Balanced Brackets (in C)

Stacks: Balanced Brackets Challenge in C

/**
The challenge:
https://www.hackerrank.com/challenges/ctci-balanced-brackets
**/

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

bool is_balanced(char expression[]) 
{
 int s = strlen(expression);
 float strlenhalf = s/2;
 int countpairs = 0;
 int difference = 0;
    
    //printf("%i \n", s);
  

    if((s %2) != 0) //not whole number or odd strlen
        {
        return 0; //false
        }
// "()" ****************************************************************************************   
    
    //iterate through string
    for(int i = 0; i < s-1; i++) //from left
        {
        //compare char by ASCII number.
        //printf("expression[i] %c \n", expression[i]);
        //printf("expression[i] numerical %i \n", expression[i]);
        //printf("check i %i \n", i);
        
        if(expression[i] == 40) //40 = "(")
            {
            
            for(int j = s-1; j > 0; j--) //from right
                {
                
                //printf("check j %i \n", j);
                
                        if(expression[j] == 41) //41 = ")"
                            {
                            expression[i] = 0;
                            expression[j] = 0;

                            difference = j- i;
                            //difference = difference %2;
                            countpairs = countpairs+1;

                            //printf("countpairs %i \n", countpairs);
                            //printf("difference %i \n", difference);

                            /*
                            if((difference %2) != 0) //even  difference between brackets. so unmatching. not included in as final condition of prototype is a comparison between strlen/2 and total pairs, which does the same thing.
                                {
                                return 0; //false
                                }
                            */
                            break;

                    }
                }            
             }
        }
     // "()" ****************************************************************************************
  // "[]]" ****************************************************************************************   
    
    //iterate through string
    for(int i = 0; i < s-1; i++) //from left
        {
        //compare char by ASCII number.
        
        if(expression[i] == 91) //40 = "[")
            {
            
            for(int j = s-1; j > 0; j--) //from right
                {
                
                
                        if(expression[j] == 93) //41 = "]"
                            {
                            expression[i] = 0;
                            expression[j] = 0;

                            difference = j- i;
                            countpairs = countpairs+1;


                            break;

                    }
                }            
             }
        }
    // "[]]" ****************************************************************************************  
    // "{}}]" ****************************************************************************************   
    
    //iterate through string
    for(int i = 0; i < s-1; i++) //from left
        {
        //compare char by ASCII number.
        
        if(expression[i] == 123) //123 = "{")
            {
            
            for(int j = s-1; j > 0; j--) //from right
                {
                
                //printf("check j %i \n", j);
                
                    if(expression[j] == 125) //125 = "}"
                            {
                            expression[i] = 0;
                            expression[j] = 0;

                            difference = j- i;
                            countpairs = countpairs+1;

                            break;

                    }
                }            
             }
        }
    // "{}" ****************************************************************************************      
    
    // END ****************************************************************************************
   // printf("totalpairs %i \n", countpairs);
    
    if(strlenhalf > countpairs)
        {
        return 0; //false
        }
    
    
    return 1;
}

int main(){
    int t; 
    scanf("%d",&t);
    for(int a0 = 0; a0 < t; a0++){
        char* expression = (char *)malloc(512000 * sizeof(char));
        scanf("%s",expression);
        
        //for loop and use is_balanced(expression[i])
         bool answer = is_balanced(expression);
         if(answer)
          printf("YES\n");
         else
          printf("NO\n");
    }
    return 0;
}

No constraints included. But 17/18. So I decided to stop here.