#include <stdio.h>
#include <ctype.h>

float num(int);/*a function that gets characters anf returns a number out of them*/
int op(void);/*a function that gets a characters and check if it is a valid mathematical operator*/
void print(float,char,float);/*a function that prints the equation*/
void claculator(void);/*a function that gets the input from the user*/
int my_math(void);

const int TEN = 10;
/*get number function*/
float num(int c)
{
	int negative= 1;
	float num1 = 0;
	float num2 = 0;
	float tens = 10.0;
	 
	while ((c != (' '))&& (c != '\n'))
	{
		if (c== '-')
			negative = -1;
  
		if (isdigit(c))
			num1 = (num1 * TEN) + (c - '0');
  
		if (c== '.')
		{
			while (isdigit((c=getchar())))
			{
				num2= num2+((c-'0') / tens);
				tens = tens * TEN;
			}
			break;
		}
		c= getchar();
	}
     
	return ((num1+num2) * negative);
}

/*get opreation function*/
int op()
{
	char ch = 0;
	while((ch=getchar())!=EOF)
	{
		if(ch==' ')/*continue the loop if the user types space*/
		{
			continue;
		}
		if(ch == '+' || ch == '-' || ch == '*' || ch == '/')/*returns the character if it is a valid mathematical operator, returns EOF otherwise*/
		{
			return ch;
		}
	}
	return EOF;/*returns EOF if the user types other character*/
}

/*print calculator function*/
void print (float n1, char op, float n2)
{
	switch(op)/*checks which mathematical operator the user entered and prints the equation*/
	{
		case '+': printf("%g + %g = %g\n",n1,n2,n1+n2);return;
		case '-': printf("%g - %g = %g\n",n1,n2,n1-n2);return;
		case '*': printf("%g * %g = %g\n",n1,n2,n1*n2);return;
		case '/': printf("%g / %g = %g\n",n1,n2,n1/n2);return;
		default: printf("invalid operator");return;
	}
	return;
}

/*calculator function*/
void calculator()
{
	char c = 0;
	float n1 = 0, n2 = 0;/*the numbers that the user types*/
	int operator = 0;/*the mathmatical operator that the user types*/
	printf("enter a string contains two operands and an operator\n");
	
	n1 = num(c);/*the first number*/
	if((operator = op())==EOF)/*the operator*/
	{
		printf("invalid operator");
		return;
	}
	n2 = num(c);/*the second number*/
	print(n1,operator,n2);/*activates the print function*/
}

int my_math()
{
	calculator();
	return 0;
}