Intermediate code generator

intercodegen.c

#include <stdio.h>
#include<string.h>
#include<ctype.h>
#define MAX_SIZE 100

char expr[MAX_SIZE] = {0};
char STACK[MAX_SIZE] = {0}, POST[MAX_SIZE] = {0};

int top=-1;
int rear=-1,front=-1;
char TEMPS='0';

void push(char x){
    top++;
    STACK[top]=x;
}
char pop(){
    char ch=STACK[top];
    top--;
    return ch;
}
int precedence(char op){
    switch(op){
        case '*':case '/': return 5; 
        case '+':case '-':return 3;
        case '=': return 2;
        default: return 1;
    }
}
void enqueue(char ch){
    rear++;
    POST[rear]=ch;
}
void createPostFix(char *expr){
    int i,len=strlen(expr);
    char op;
    for(i=0;i<len;i++){
        if(isalpha(expr[i])){
            enqueue(expr[i]);
        }
        else{
            switch(expr[i]){
                case '(':push(expr[i]);break;
                case ')':while(STACK[top]!='('){
                    enqueue(pop());
                }break;
                default:
                    while(precedence(expr[i]) <= precedence(STACK[top])){
                        enqueue(pop());
                    }
                    push(expr[i]);
            }
        }
    }
    while(top!=-1){
        op=pop();
        if(op!='(')
            enqueue(op);
    }
}
char getTemp(){
    return TEMPS++;
}
void printCode(int i){
    char operand1,operand2,operator;
    operand2=pop();
    operand1=pop();
    operator=POST[i];
    if(operator=='='){
    	printf("%c = %c \n",operand1,operand2);
    	return;
    }
    char newTemp=getTemp();
    push(newTemp);
    printf("%c = %c %c %c\n",newTemp,operand1,operator,operand2	);
}
int main(){
    int len,i;
    scanf("%s", expr);
    createPostFix(expr);
    len=strlen(POST);
    for(i=0;i<top;i++){
    	STACK[i]=0;
    }
    for(i=0;i<len;i++){
        if(isalpha(POST[i])){
        	push(POST[i]);
        }
        else{
            printCode(i);
        }
    }

    // printf("\n%s : %lu\n", POST, strlen(POST));
    // printf("%s\n", STACK);
    return 0;
}