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checks the well formness of the parentheses

Discussion in 'C' started by JamesBond, Oct 15, 2006.

  1. JamesBond

    JamesBond New Member

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    Introduction



    The idea is simple just to test whether the expression contains correct sequence of brackets or not.

    Code:
    void main()
    {
    	char arr[N];
    	char *top;
    	int loop=0,i,l,binary;
    
    	printf("Enter expression of brackets for checking its correctness\n");
    
    	gets(arr);
    
    	top=stack;
    	l=strlen(arr);
    
    	for(i=0;i<l;i++)
    	{
    		if(arr[i]=='('||arr[i]=='['||arr[i]=='{')
    			binary=push(&top,arr[i],&loop);		/**  Returns 0 if incorrect  **/
    		else if(arr[i]==')'||arr[i]==']'||arr[i]=='}')
    			binary=pop(&top,arr[i],&loop);		/***  Returns 1 if correct  ***/
    		if(binary==0)
    			break;
    	}
    
    	if(top==stack && binary==1)
    	{
    		printf("YES. The above expression is Correct\n");
    	}
    	else
    	{
    		printf("NO. The above expression is Incorrect\n");
    	}
    }
    

    How it is done



    Using stack. Just push "{", "[", "(" when found and pop when the closing one is found. Remember while popping you match into the stack content to have the same pair of closing and opening.

    The helper functions



    The push Function
    Code:
    int push(char **top,char arr,int *loop)     /** PUSH FUNCTION **/
    {
    	if(*loop==N)		/**  loop is must for this checking  **/
    		return(0);
    	else
    	{
    		(*loop)++;
    		**top=arr;
    		(*top)++;
    		return(1);
    	}
    }
    
    The Pop Function
    Code:
    int pop(char **top,char arr,int *loop)      /** POP FUNCTION **/
    {
    	if(*loop==0)
    		return(0);
    	switch(arr)
    	{
    	case ')':
    		arr='(';
    		break;
    	case '}':
    		arr='{';
    		break;
    	case ']':
    		arr='[';
    		break;
    	}
    	(*top)--;		/**  For checking that the same bracket is closed  **/
    	if(**top!=arr)
    		return(0);
    	else
    	{
    		(*loop)--;
    		return(1);
    	}
    }
    
    Note : See the switch case in the pop to gurantee the pairing of braces / brackets
     
  2. aisha.ansari84

    aisha.ansari84 New Member

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    i didnt get you
     
  3. rahul.mca2001

    rahul.mca2001 New Member

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