ADT_Array_as_Stack_infix_to_prefix_postfix.c

// author: jaydattpatel
#include<stdio.h>
#include<ctype.h>

char stack[100];
int top = -1;

void push(char x)
    {stack[++top] = x;}

char pop()
{
    if(top == -1)   return(-1);
    else    return(stack[top--]);
}

int priority(char x)
{
    if(x == '(')    return 0;
    if(x == '+' || x == '-')    return 1;
    if(x == '*' || x == '/')    return 2;
    return 0;
}

int main()
{
    char exp[100];
    char *e, x;
    printf("Enter the expression : ");
    scanf("%s",exp);
    printf("\n");
    e = exp;
    
    while(*e != '\0')
    {
        if(isalnum(*e))     printf("%c ",*e);
        else if(*e == '(')  push(*e);
        else if(*e == ')')
            {
                while((x = pop()) != '(')   printf("%c ", x);
            }
        else
        {
            while(priority(stack[top]) >= priority(*e))
                    printf("%c ",pop());
            push(*e);
        }
        e++;
    }
    
    while(top != -1)      printf("%c ",pop());
    
    return 0;
}