C program for infix expression to postfix expression and postfix expression evaluation

C program for infix expression to postfix expression and postfix expression evaluation

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
void push1(char);
char pop1(void);
int operand(char);
int priority(char);
void push2(float);
float pop2(void);
float findval(char);
char expr[100];
char variable[100];
float value[100];
char stack1[100],c;
int top1=-1;
int top2=-1;
char postfix[100];
int nv;
float stack2[100];
float val,val1,val2;
main()
{
 int i,j,l,p1,p2,flag;
 printf("Enter the no. of variables\n");
 scanf("%d",&nv);
 printf("Enter the variable names\n");
 getchar();
 for(i=0;i<nv;i++)
 {
  scanf("%c",&variable[i]);
  getchar();
 }
 printf("enter the values of variables\n");
 for(i=0;i<nv;i++)
 {
  printf("%c=?",variable[i]);
  scanf("%f",&value[i]);
 }
 printf("enter the infix expression\n");
 scanf("%s",expr);
 l=strlen(expr);
 expr[l]=')';
 expr[l+1]='\0';
 push1('(');
 i=0;
 j=0;
 while(top1>=0)
 {
  if(operand(expr[i]))
  {
   postfix[j++]=expr[i];
  }
  else if(expr[i]=='(')
  {
   push1('(');
  }
  else if(expr[i]==')')
  {
   c=pop1();
   while(c!='(')
   {
    postfix[j++]=c;
    c=pop1();
   }
  }
  else
  {
   p2=priority(expr[i]);
   p1=priority(stack1[top1]);
   while(p1>=p2)
   {
    postfix[j++]=pop1();
    p1=priority(stack1[top1]);
   }
   push1(expr[i]);
  }
  i++;
 }
 postfix[j]='\0';
 printf("Postfix expression=%s",postfix);
 printf("\n");
 i=0;
 for(i=0;postfix[i]!='\0';i++)
 {

  if(operand(postfix[i]))
  {
   val=findval(postfix[i]);
   push2(val);
  }
  else
  {
   val1=pop2();
   val2=pop2();
   switch(postfix[i])
   {
    case '+':
     val=val2+val1;
     break;
    case '-':
     val=val2-val1;
     break;
    case '*':
     val=val2*val1;
     break;
    case '/':
     val=val2/val1;
     break;
    case '^':
     val=pow(val2,val1);
     break;
    default:
     {
      printf("Error!\n");
      exit(0);
     }
   }  
   push2(val);
  }
 }
 val=pop2();
 printf("The value of expression=%f",val);
 printf("\n");
}
void push1(char c)
{

 stack1[++top1]=c;
}

char pop1(void)
{
 char c;
 c=stack1[top1];
 top1--;
 return c;
}
void push2(float c)
{
 stack2[++top2]=c;
}
                           
float pop2(void)
{
 float c;
 c=stack2[top2];
 top2--;
 return c;
}
int operand(char c)
{
 int i,flag=0;
 for(i=0;i<nv;i++)
 {
  if(variable[i]==c)
  { 
   flag=1;
  }
 }
 return flag;
}
int priority(char c)
{
 if(c=='(')
 {
  return 0;
 }
 if(c=='+')
 {
  return 1;
 }
 if(c=='-')
 {
  return 1;

 }
 if(c=='*')
 {
  return 2;
 }
 if(c=='/')
 {
  return 2;
 }
 if(c=='^')
 {
  return 3;
 }
 else
 {
  printf("Invalid operation\n");
  exit(0);
 }
}
float findval(char c)
{
 int i;
 for(i=0;i<nv;i++)
 {
  if(c==variable[i])
  {
   return value[i];
  }
  
 }
  return 0;
}

Output