Stack_Parentheses_balanced

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

int is_balanced(char input[])
{
    char stack[100],last_char;
    int top,i,len;

    top=0;
    len=strlen(input);

    for(i=0;i<len;i++){
        if(input[i]=='('){
            stack[top]='(';
            top++;
           }
           else if(input[i]==')'){
            if(top==0){
                return 0;
            }
            top--;
            last_char=stack[top];
            if(last_char!='('){
                return 0;
               }
           }
    }
    if(top==0){
        return 1;
    }else {
    return 0;}
}

int main()
{
    char input[100];
    scanf("%s", input);
    if(is_balanced(input)){
        printf("%s is balanced\n",input);
    }else {
        printf("%s is not balanced\n",input);
    }
    return 0;
}