INFIX to POSTFIX

/* INPIX TO POSITPIX or EVALUATION */

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

#define MAX_STACK_SIZE 100
#define MAX_EXRP_SIZE 100

typedef enum {
lparen, rparen, plus, minus, times, divide, mod, positive, negative, eos, operand
} precedence;

enum {
single, couple
} preop;

int isp[] = { 0, 0, 1, 1, 2, 2, 2, 3, 3, 0, 0};
int icp[] = { 9, 0, 1, 1, 2, 2, 2, 4, 4, 0, 0};
char operator[] = {' ', ' ', '+', '-', '*', '/', '%', '\0', ' '};

char expr_1[MAX_EXRP_SIZE];
char expr_2[MAX_EXRP_SIZE];
double calc_stack[MAX_STACK_SIZE];

void postfix(void);
double calc(void);
precedence get_token(char *, int *);

main()
{
char str[20];
int i;

while(str[0]!='E' && str[1] !='N' && str[2]!='D'
&& str[3]!='-' && str[4]!='O' && str[5]!='F'
&& str[6]!='-' && str[7]!='I' && str[8]!='N'
&& str[9]!='P' && str[10]!='U' && str[11]!='T')
{
system("cls");
printf("\t CALCULATION PROGRAM \n\n");
printf("INPUT STRING : ");
i=-1;

while( (expr_1[++i]=getchar()) != '$' );
expr_1[i]='\0';
postfix();
printf("\nRESULT IN POSTFIX : %s\n\n", expr_2);
printf("RESULT IN CALCULATION : %lf\n\n", calc());
scanf("\n%s", &str);
}
}

void postfix(void)
{
precedence stack[MAX_STACK_SIZE];
char symbol;
int n=0,j=0;
int top=0;
precedence token;
stack[0]=eos;

preop=single;

for(token=get_token(&symbol,&n);token!=eos;token=get_token(&symbol,&n))
{
if(token==operand)
expr_2[j++]=symbol;
else if(token==rparen) {
while(stack[top]!=lparen) {
expr_2[j++]=' ';
expr_2[j++]=operator[stack[top--]];
}
top--;
}
else {
while( isp[stack[top]] >= icp[token] ) {
expr_2[j++]=' ';
expr_2[j++]=operator[stack[top--]];
}
stack[++top]=token;
expr_2[j++]=' ';
}
}
while( (token=stack[top--]) != eos ) {
expr_2[j++]=' ';
expr_2[j++]=operator[token];
}
expr_2[j++]=operator[token];
}

precedence get_token(char *symbol, int *n)
{
*symbol=expr_1[(*n)++];
switch(*symbol)
{
case '(' : return lparen;
case ')' : preop=couple; return rparen;
case '+' : if(preop==single)
return positive;
else {
preop=single;
return plus;
}
case '-' : if(preop==single)
return negative;
else {
preop=single;
return minus;
}
case '*' : preop=single;
return times;
case '/' : preop=single;
return divide;
case '%' : preop=single;
return mod;

case ' ' : preop=single;
return operand;
case '\t': preop=single;
return operand;
case '\0': preop=single;
return eos;
default : preop=couple;
return operand;
}
}

double calc()
{
char *p=expr_2;
int top=-1;

while(*p != '\0') {
if( (*p>='0' && *p<='9') || (*p=='.') ) {
calc_stack[++top]= atof(p);
while(*(p++) != ' ');
}
else
switch (*p)
{
case '+' :
if(top < 0) {
printf("stack empty\n");
exit(1);
}
else {
calc_stack[top]=calc_stack[--top] + calc_stack[top+1];
p++;
break;
}
case '-' :
if(top < 0) {
printf("stack empty\n");
exit(1);
}
else {
calc_stack[top]=calc_stack[--top] - calc_stack[top+1];
p++;
break;
}
case '*' :
if(top < 0) {
printf("stack empty\n");
exit(1);
}
else {
calc_stack[top]=calc_stack[--top] * calc_stack[top+1];
p++;
break;
}
case '/' :
if(top < 0) {
printf("stack empty\n");
exit(1);
}
else if(calc_stack[top]==0) {
printf("WRONG INPUT!!\n");
exit(1);
}
calc_stack[top]=calc_stack[--top] / calc_stack[top+1];
p++;
break;
case '%' :
if(top < 0) {
printf("stack empty\n");
exit(1);
}
else {
calc_stack[top]=(int)calc_stack[--top] % (int)calc_stack[top+1];
p++;
break;
}
default : p++;
}
}
return calc_stack[top];
}