C++ Programming Exercise: Implement a command-line calculator that allows the us
ID: 645674 • Letter: C
Question
C++ Programming Exercise:
Implement a command-line calculator that allows the user to enter an expression containing numbers, variables, brackets, and operators. The calculator will also allow assignments to a variable. After the user enters the expression the program will evaluate it and display the value. If the expression is part of an assignment its value will be also be stored in the variable. The operators are +, -, *, /, % and ^ (exponentiation). (These are all binary operators.) % should be applicable to floating point numbers and work like it does in Java. There are three types of bracket: parentheses ( ( ) ) , square brackets ( [ ] ) and braces ( {} ). A variable may be any single lowercase letter. (Uninitialized variables can have any value.) The calculator will loop until the user enters a blank line. Here is a sample run below:
> 3 + 4.5
7.5
> a = 6*2/5
2.4
> b = a+1
3.4
> b
3.4
> c = b^2
11.56
> a * {b
Explanation / Answer
// calculator_2.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
#include <cmath>
#include <stack>
using namespace std;
stack<char> st;
stack<double> sti;
char var[20];
double data[20];
int no_of_var=0;
struct exp
{
char type;
double val;
}e[100];
int i=0;
int priority ( char c )
{
if ( c == '^' )
return 3 ;
if ( c == '*' || c == '/' || c == '%' )
return 2 ;
else
{
if ( c == '+' || c == '-' )
return 1 ;
else
return 0 ;
}
}
double search(char c,int *fl)
{
int j=0;
for(j=0;j<no_of_var;j++)
if(var[j]==c)
{
*fl=j;
return data[j];
}
*fl=-1;
return -1;
}
void create(char *s, double v)
{
double n;
int fl;
n = search(*s,&fl);
if(fl>=0)
{
var[fl] = *s;
data[fl] = v;
}
else
{
var[no_of_var] = *s;
data[no_of_var++] = v;
}
}
void convert(char *s )
{
char temp[100];
char *t = temp;
double n,d;
int fl;
i=0;
while ( *s )
{
if(*s==' ')
s++;
if ( isdigit ( *s ) || *s=='.')
{
n=0;d=1;
while ( isdigit ( *s ) )
{
n = n*10+ (*s-'0') ;
s++ ;
}
if(*s=='.')
{
s++;
while(isdigit ( *s ))
{
n = n + (*s-'0')/pow(10,d++);
s++;
}
}
e[i].type='n';
e[i++].val=n;
}
if(isalpha(*s))
{
n = search(*s++,&fl);
if(fl==-1)
{
cout<<" Variable not found !!";
return;
}
e[i].type='n';
e[i++].val=n;
}
if ( *s == '(' || *s == '[' || *s == '{')
{
st.push ( *s ) ;
s++ ;
}
char opr ;
if ( *s == '*' || *s == '+' || *s == '/' || *s == '%' || *s == '-' || *s == '^' )
{
if ( !st.empty() )
{
opr = st.top() ;
st.pop();
while ( priority ( opr ) >= priority ( *s ) && !st.empty() )
{
e[i].type='o';
e[i++].val=opr;
opr = st.top() ;
st.pop();
}
st.push ( opr ) ;
st.push ( *s ) ;
}
else
st.push ( *s ) ;
s++ ;
}
if ( *s == ')' )
{
opr = st.top( ) ;
st.pop();
while ( ( opr ) != '(' )
{
e[i].val = opr ;
e[i++].type='o';
opr = st.top( ) ;
st.pop();
}
s++ ;
}
if ( *s == ']' )
{
opr = st.top( ) ;
st.pop();
while ( ( opr ) != '[' )
{
e[i].val = opr ;
e[i++].type='o';
opr = st.top( ) ;
st.pop();
}
s++ ;
}
if ( *s == '}' )
{
opr = st.top( );
st.pop();
while ( ( opr ) != '{' )
{
e[i].val = opr ;
e[i++].type='o';
opr = st.top( ) ;
st.pop();
}
s++ ;
}
}
while ( !st.empty() )
{
char opr = st.top();
st.pop();
e[i].val = opr ;
e[i++].type='o';
}
}
void clear()
{
while(!st.empty())
st.pop();
while(!sti.empty())
sti.pop();
}
double calculate()
{
clear();
int j=0;
double n1, n2, n3,nn ;
while (j<i)
{
if ( e[j].type=='n' )
{
sti.push ( e[j].val ) ;
}
else
{
n1 = sti.top( ) ;
sti.pop();
n2 = sti.top( ) ;
sti.pop();
switch ( char(e[j].val) )
{
case '+' :
n3 = n2 + n1 ;
break ;
case '-' :
n3 = n2 - n1 ;
break ;
case '/' :
n3 = n2 / n1 ;
break ;
case '*' :
n3 = n2 * n1 ;
break ;
case '%' :
n3 = int(n2) % int(n1) ;
break ;
case '^' :
n3 = pow ( n2 , n1 ) ;
break ;
default :
cout << "Unknown operator" ;
exit ( 1 ) ;
}
sti.push ( n3 ) ;
}
j++ ;
}
return sti.top();
}
int chk(char *s)
{
double v;
char *t;
t = s;
while(*s)
{
if(*s=='-'&& ( *(s+1) >= 'a' && *(s+1) <= 'z' ))
{
cout<<" - as unary operator not allowed !!";
return -1;
}
s++;
}
s = t;
while(*s)
{
if(*s++ == '=')
{
if(*t >='a' && *t <= 'z')
{
convert(s);
v = calculate();
create(t,v);
return 1;
}
else
{
cout<<" Only lower case letters allowed !";
return -1;
}
}
}
return 0;
}
int main( )
{
char expr[100] ;
int r;
while(1)
{
cout<<" >";
cin.getline ( expr, 100 ) ;
if(strlen(expr)==0)
break;
r = chk(expr);
if(r==0)
convert(expr);
for(int j=0;j<i;j++)
{
if(e[j].type=='n')
cout << e[j].val;
else
cout << char(e[j].val);
}
cout<<endl<<calculate();
// else if(r==1)
}
}
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