postfix.c

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

typedef struct Stack
{
    char* elements;
    int size;
    int capasity;
}stack;

stack* s; //Globally declearing stack pointer

//Declearing functions...

void postfix(char arr[]);
int count(char* arr);

/*Star of stack functions */

void creatstack(int size)
{
    s=(stack*)malloc(sizeof(stack));
    s->elements=(char*)malloc(sizeof(char)*size);
    s->capasity=size;
    s->size=0;
}

void push(char data)
{
    if(s->size==s->capasity)
    {
        printf("\nStack is full");
    }
    else
    {
        s->elements[s->size++]==data;
    }
}

char top()
{
    if (s->size==0)
    {
        printf("\nStack is Empty");
    }
    return s->elements[s->size-1];
}

void pop ()
{
    if (s->size==0)
    {
        printf("\nStack is Empty");
    }
    else
    {
        s->size--;
    }

}

/* End of stack functions */

void main()
{
    int stacksize;
    char expression[20];
    printf("Input your expression: ");
    gets(expression); //Input string
    stacksize=count(expression); //Getting the size of stack
    creatstack(stacksize); // creating a stack of the size 
    char temp[20]; 
    strcpy(temp,expression); //
    postfix(temp);

}
void postfix(char arr[])
{
    int i,j,k;
    i=j=k=0;
    char temp[20];
    push('(');
    while (arr[i]!='\0')
    {
        if (arr[i]=='(')
        {
            push(arr[i]);
            i++;
            continue;
        }
        else if (arr[i]>='a' && arr[i]<='z')
        {
            temp[j]=arr[i];
            i++;
            j++;
            continue;
        }
        else if (arr[i]=='*' ||arr[i]=='/')
        {
            while (top()=='*' || top()=='/' || top()=='+'||top()=='-')
                {
                    temp[j]=top();
                    pop();
                    j++;
                }
                if (top()=='(')
                {
                    push(arr[i]);
                    i++;
                    continue;
                }
        }
        else if (arr[i]=='+' ||arr[i]=='-')
        {
            while (top()=='*' || top()=='/')
            {
                temp[j]=top();
                pop();
                j++;
            }
            if (top()=='+' || top()=='-'|| top()=='('|| top()==')')
            {
                push(arr[i]);
                i++;
                continue;
            }
        }
        if (arr[i]==')')
        {
            while (top()!='(')
            {
                temp[j]=top();
                pop();
                j++;
            }
            push(arr[i]);
            i++;
            continue;
        }
    }
    strcpy(arr,temp);
    printf("\n");
    puts(arr);
}

int count(char* arr)
{
    int i,c;
    i=c=0;
    while (*(arr+i)!='\0')
    {
        if (*(arr+i)=='+'|| *(arr+i)=='-'||*(arr+i)=='*'||*(arr+i)=='/'||*(arr+i)=='('||*(arr+i)==')'||*(arr+i)=='^')
        {
            c++;
            i++;
        }
        else
            i++;
    }
    return i;
}