C++ source code: for creating a simple CALCULATOR

#include
#include"math.h"
#include"stdlib.h"
#include"string.h"
#include"ctype.h"
#define rad 0.017453292
struct stack1
{
char item;
stack1 *next;
};


stack1 *push1(stack1 *hd,char m)
{
stack1 *ptr;
if(!(ptr=(stack1*)malloc(sizeof(stack1))))
{
cout<<"OVERFLOW";
exit(0);
}
else
{
ptr->item=m;
ptr->next=hd;
hd=ptr;
}
return hd;
}


stack1 *pop1(stack1* hd,char* v)
{
stack1 *ptr;
if(hd==NULL)
{
cout<<"\n\nEXPRESSION ERROR\n";
exit(0);
}
else
{
*v=hd->item;
ptr=hd;
hd=hd->next;
free(ptr);
}
return hd;
}

// **STACK2** [ used for evaluating the postfix expression ]

struct stack2
{
double item;
stack2 *next;
};
stack2 *push2(stack2 *hd,double m)
{
stack2 *ptr;
if(!(ptr=(stack2*)malloc(sizeof(stack2))))
{
cout<<"OVERFLOW";
exit(0);
}
else
{
ptr->item=m;
ptr->next=hd;
hd=ptr;
}
return hd;
}


stack2 *pop2(stack2* hd,double* v)
{
stack2 *ptr;
if(hd==NULL)
{
cout<<"\n\nEXPRESSION ERROR\n";
exit(0);
}

else
{
*v=hd->item;
ptr=hd;
hd=hd->next;
free(ptr);
}
return hd;
}

/* **MAKE_OPERAND** [ function used for converting the
operands from string to double ] */
double make_operand(char acore[] )
{
double sum=0;
int n=0;
for(int i=0;acore[i]!='\0';i++)
{
if(acore[i]=='.')
{
n=i+1;
continue;
}
sum=sum*10+acore[i]-48;
}
if(n>0)
sum=sum/pow(10,i-n);
return sum;
}

/* **CLASS CAL**[ contains the input equation(eqn),postfix equation
(pol),result(result) and functions for postfixing
(polish),and evaluating(evaluate) the equation . ] */
class cal
{
char eqn[100],pol[100][100];
double result;
public:
void geteqn(char*);
void polish();
void evaluate();
void pr_pole();
};
void cal::geteqn(char c[])
{
strcpy(eqn,c);
}

// **POLISH**[function used for postfixing the equation.]

void cal::polish()
{
stack1 *head=NULL;
int m,v=0,error_check=0;
head=push1(head,'(');
m=strlen(eqn);
eqn[m]=')';
eqn[m+1]='\0';
for(int i=0;eqn[i]!='\0';i++)
{
if(isdigit(eqn[i])||eqn[i]=='.')
{
for(int j=0;;j++)
{
if(isdigit(eqn[i])||eqn[i]=='.')
{
pol[v][j]=eqn[i];
i++;
}
else
{
i--;
pol[v][j]='\0';
v++;
break;
}
}
}
if(isalpha(eqn[i]))
{
int n=0;
for(int j=0;;j++)
{
if(eqn[i]=='(')
n++;
if(isdigit(eqn[i])||isalpha(eqn[i])||eqn[i]=='.'||n!=0)
{
pol[v][j]=eqn[i];
if(eqn[i]==')')
n--;
i++;
}
else
{
i--;
pol[v][j]='\0';
v++;
break;
}
}
}
else if(eqn[i]=='(')
{
head=push1(head,'(');
error_check++;
}
else if(eqn[i]=='+'||eqn[i]=='-'||eqn[i]=='*'||eqn[i]=='/'||eqn[i]=='%'||eqn[i]=='^')
{
if(eqn[i]=='+'||eqn[i]=='-')
{
while(head->item!='(')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=push1(head,eqn[i]);
}
else if(eqn[i]=='*')
{
while(head->item!='('&&head->item!='+'&&head->item!='-')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=push1(head,eqn[i]);
}
else if(eqn[i]=='/')
{
while(head->item!='('&&head->item!='+'&&head->item!='-'&&head->item!='*')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=push1(head,eqn[i]);
}
else if(eqn[i]=='%')
{
while(head->item!='('&&head->item!='+'&&head->item!='-'&&head->item!='*'&&head->item!='/')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=push1(head,eqn[i]);
}
else if(eqn[i]=='^')
{
while(head->item!='('&&head->item!='+'&&head->item!='-'&&head->item!='*'&&head->item!='/'&&head->item!='%')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=push1(head,eqn[i]);
}
}
else if(eqn[i]==')')
{
error_check--;
char c;
while(head->item!='(')
{
head=pop1(head,&pol[v][0]);
pol[v][1]='\0';
v++;
}
head=pop1(head,&c);
}
}
if(error_check!=-1)
{
cout<<"\n\nEXPRESSION ERRORs\n";
exit(0);
}
pol[v][0]='\0';
}

// **EVALUATE**[function used for evaluating the equation.]

void cal::evaluate()
{
stack2 *head=NULL;
for(int i=0;pol[i][0]!='\0';i++)
{
if(isdigit(pol[i][0])||pol[i][0]=='.')
head=push2(head,make_operand(pol[i]));
else if(isalpha(pol[i][0]))
{
char trigo[4],rest[100];
double para;
for(int j=0;isalpha(pol[i][j]);j++)
trigo[j]=pol[i][j];
trigo[j]='\0';
for(int k=0;pol[i][j]!='\0';j++,k++)
rest[k]=pol[i][j];
rest[k]='\0';
if(rest[0]=='(')
{
cal Y;
Y.geteqn(rest);
Y.polish();
Y.evaluate();
para=Y.result;
}
else
para=make_operand(rest);
if(!strcmp("tan",trigo))
{
if((int)para%180!=90)
{
cout<<"\n\nMATH ERROR\n";
exit(0);
}
else if((int)para%180!=0)
head=push2(head,tan(para*rad));
else
head=push2(head,0.0);
}
else if(!strcmp("sin",trigo))
{
if((int)para%180!=0)
head=push2(head,sin(para*rad));
else
head=push2(head,0.0);

}
else if(!strcmp("cos",trigo))
{
if((int)para%180!=90)
head=push2(head,cos(para*rad));
else
head=push2(head,0.0);
}
else if(!strcmp("log",trigo))
head=push2(head,log10(para));
else if(!strcmp("ln",trigo))
head=push2(head,log(para));
}
else
{
double opp1,opp2;
head=pop2(head,&opp1);
head=pop2(head,&opp2);
if(pol[i][0]=='+')
head=push2(head,opp2+opp1);
else if(pol[i][0]=='-')
head=push2(head,opp2-opp1);
else if(pol[i][0]=='*')
head=push2(head,opp2*opp1);
else if(pol[i][0]=='/')
{
if(opp1==0)
{
cout<<"\n\nMATH ERROR\n";
exit(0);
}
else
head=push2(head,opp2/opp1);
}
else if(pol[i][0]=='%')
{
if(opp1==0)
{
cout<<"\n\nMATH ERROR\n";
exit(0);
}
head=push2(head,(int)opp2%(int)opp1);
}
else if(pol[i][0]=='^')
head=push2(head,pow(opp2,opp1));
}
}
head=pop2(head,&result);
}

void cal:: pr_pole()
{
cout<<"\n\nRESULT:"<}

//MAIN FENCTION

void main()
{
cal X;
char c[100];
cout<<"\n\n*** you can do the operation of +,-,*,/,%,^,sin,cos,tan,log and ln ***"
<<"\n\ngive the equation:\n";
cin>>c;
X.geteqn(c);
X.polish();
X.evaluate();
X.pr_pole();
}