PROGRAM WHICH ACCEPTS AN EXPRESSION AND EVALUATES IT

Question:

Write a program that accepts an expression and evaluates it.

Hint:

For the purpose of simplicity, the following assumptions can be taken:

1. Symbols representing operations are one character long.
2. All operations are binary operations.
3.  Input is in infix format.

Solution:

/**********************************************************************************/

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

int Remove(float*,char*,int,int);

int check(char ,float*,char*,int );

void print(float*,char*,int);

int main()

{

                char str[200],*ops;

                int number=0,c_number,i,j;

                float*num;

                clrscr();

                printf("ENTER THE EXPRESSION : \n");

                printf("THE EXPRESSION SHOULD BE IN INFIX FORMAT AND SHOULD NOT INCLUDE SPACES...\n");

                scanf("%s",str);

                i=0;

                while(str[i])

                {

                                if((int)str[i]<48||(int)str[i]>57)

                                                number++;

                                i++;

                }

                number++;

                //number stores the total number of operands

                num=(float*)malloc(sizeof(float)*(number));

                ops=(char*)malloc(sizeof(char)*(number-1));

                for(i=0;i<number;i++)

                                num[i]=0;

                i=j=0;

                while(str[i])

                {

                                if((int)str[i]<48||(int)str[i]>57)

                                                ops[j++]=str[i];

                                i++;

                }

                i=j=0;

                while(str[i])

                {

                                while(((int)str[i]>=48&&(int)str[i]<=57))

                                                num[j]=num[j]*10+(int)str[i++]-48;

                                i++;j++;

                }

                c_number=number;

                for(i=0;i<c_number-1;i++)

                {

                                number=check('/',num,ops,number);

                                number=check('*',num,ops,number);

                                number=check('-',num,ops,number);

                                number=check('+',num,ops,number);

                }

                printf("\n\nFinal Answer = %g\n",num[0]);

                getch();

                return 1;

}

int check(char op,float*num,char*ops,int number)

{

                int j;

                while(1)

                {

                                j=0;

                                while(ops[j]!=op&&j<number)

                                {

                                                j++;

                                                if(j>number-1)

                                                                break;

                                }

                                if(j>number-1)

                                                return number;

                                if(j<number-1)

                                {

                                                if(op=='/')

                                                                num[j]=num[j]/num[j+1];

                                                else if(op=='*')

                                                                num[j]=num[j]*num[j+1];

                                                else if(op=='+')

                                                                num[j]=num[j]+num[j+1];

                                                else

                                                                num[j]=num[j]-num[j+1];

                                                number=Remove(num,ops,j,number);

                                                continue;

                                }

                                break;

                }

                return number;

}

void print(float*num,char*ops,int number)

{

                int i;

                for(i=0;i<number-1;i++)

                                printf("%g %c ",num[i],ops[i]);

                printf("%g\n",num[i]);

}

int Remove(float *num,char *ops,int j,int number)

{

                int i;

                for(i=j+1;i<number-1;i++)

                {

                                num[i]=num[i+1];

                                ops[i-1]=ops[i];

                }

                number--;

                print(num,ops,number);

                return number;

}

/**********************************************************************************/