infix to postfix conversion using stack(half-way)

#include<stdio.h>
#include<ctype.h>
//our task is to convert infix to postfix expression using stack

//first we need a stack 
//let's define it 

char s[max]; 
int val; //here val is value to be pushed to the stack

 //define a top pointer for stack
 int top=-1;
//defining a string array for storing the entered infix string 
char exp[100];

//defining functions
//this functions may be required
// basic stack functions
void push(void);
void pop(void);

//start main function of the program
int main()
{
printf("Enter any postfix expression:\n");
gets(exp);
val=evaluateposfix(exp);
return 0;
}
//infixtopostfix() function
void infixtopostfix(void)
{

/*

START FROM HERE GUYS :)

*/

}

void push(void)
{
//for pushing or inserting an element we check overflow condition
if(x==max-1)
    {
    printf("Error : Stack Overflow\n");
    }
 //incrementing the pointer   
top++;
//finally pushing or inserting the value in stack.
s[top]=x;

}


void pop(void)
{
//for pop function we first check underflow conditions
if(top==max-1)
    {
    printf("Error : Stack Under Flow");
    
    }
//decrementing the top pointer for deletion of element
    top--;

}