infix

#include <stdio.h>
#include <ctype.h>
#include <string.h>
#define MAX 50
char stack[MAX];
int top=-1;

int precedence(char item){
    if(item=='-' || item=='+')
        return 1;
    if(item=='*' || item=='/')
        return 2;
    if(item=='^')
        return 3;
    if(item=='(')
        return 0;
    return -1;
}
int isOperand(char ch){
    if(isdigit(ch) || islower(ch) || isupper(ch)){
        return 1;
    }
    else
        return 0;
}
void push(char input){
    if(top==MAX-1){
        printf("\nStack Overflow\n");
    }
    else{
        stack[++top]=input;
    }
}
int pop(){
    char item;
    if(top==-1){
        printf("\nStack Underflow\n");
        return -1;
    }
    else{
        item=stack[top--];
    }
    return item;
}
char str[2];
char* getStr(char ch){
    str[0]=ch;
    str[1]='\0';
    return str;
}
void infixToPostfix(char exp[],char output[]){
    int n=strlen(exp);
    for(int i=0;i<n;i++){
        if(isOperand(exp[i])){
            strcat(output,getStr(exp[i]));
        }
        else if(exp[i]=='('){
            push(exp[i]);
        }
        else if(exp[i]==')'){
            while(stack[top]!='('){
                strcat(output,getStr(pop()));
            }
            pop();
        }
        else{
            while(top!=-1 && precedence(exp[i])<=precedence(stack[top])){
                    strcat(output,getStr(pop()));
            }
            push(exp[i]);
        }
    }
    if(top!=-1){
        for(int i=top;exp[i]!=0;--i){
            strcat(output,getStr(stack[i]));
        }
    }
}

int main(){
    char exp[MAX],output[MAX];
    output[0]='\0';
    printf("Enter the expression:\n");
    scanf("%s",exp);
    infixToPostfix(exp,output);
    printf("\nPostfix expression is %s\n",output);
}