Question

Create a C program Evaluate an expression from console input and print its result.

-The format of expressions: Number Symbol Number Symbol ... Symbol Number = Number

-Number refers to an integer and Symbol refers to either + , -, *, or / - * and / have higher priority over + and

-. E.g., given input “1+2*3+4=”, the result should be “11”; Hint: Use Polish Notation

Answer 1

#include<stdio.h> char expr[20];//array to store entered expression char stack[20];//store the postfix expression int precedence(char a,char b) {//returns true if precedence of operator a is more or equal to than that of b if(((a=='+')||(a=='-'))&&((b=='*')||(b=='/'))) return 0; else return 1; } int i; int ctr; int top=-1;//top of postfix stack int topOper=-1;//top of operator stack int operate(int a,int b,char oper) { int res=0; switch(oper) { case '+':res=a+b;break; case '-':res=a-b;break; case '*':res=a*b;break;//return result of evaluation case '/':res=a/b;break; } return res; } void postfixConvert() { char topsymb,operatorStack[20]; ctr=0; while(expr[ctr]!='\0') {//read till the end of input if(expr[ctr]>='0'&&expr[ctr]<='9') stack[++top]=expr[ctr];//add numbers straightaway else { while(topOper>=0&&precedence(operatorStack[topOper],expr[ctr])) {//check for the operators of higher precedence and then add them to stack topsymb=operatorStack[topOper--]; stack[++top]=topsymb; } operatorStack[++topOper]=expr[ctr]; } ctr++; } while(topOper>=0)//add remaining operators to stack stack[++top]=operatorStack[topOper--]; printf("The Resulting Postfix expression for the given infix expression\n%s\n",stack); } int main() { printf("\t\tExpression Evaluator\n"); printf("This Program Evaluates Basic Expressions(without brackets) with arithmetic operations(+,-,*,/) on single digit operand length below 20\n"); printf("Enter the Expression\n"); scanf("%s",expr); postfixConvert();//function to convert in postfix form char oper; int operand1,operand2; ctr=0; int result[2];//stack to keep storing results int rTop=-1;//top of result stack while(stack[ctr]!='\0') { oper=stack[ctr]; if(oper>='0'&&oper<='9') result[++rTop]=(int)(oper-'0');//add numbers else {//if an operator is encountered than pop twice and push the result of operation to the stack operand1=result[rTop--]; operand2=result[rTop--]; result[++rTop]=operate(operand2,operand1,oper); } ctr++; } printf("The result of the expression is\n%d\n",result[0]); getch(); }