C language implementation of a calculator and C language implementation of a calculator

C language implementation of a calculator and C language implementation of a calculator

Today, I read compilation principles and practices and saw the implementation of a simple Integer Calculator.

Based on the ideas in the book, I made some extensions:

1. Extend From Integer Calculator to decimal calculator.

2. Division is supported.

3. Empty characters are supported.

The running effect is as follows:

The Code is as follows:

Cal. c:

#include <stdio.h>#include <stdlib.h>char token;double exp(void);double term(void);double factor(void);char getPrintableChar(void);void match(char expectedToken);void error(void);int main(void){double result;for (;;){token = getPrintableChar();if (token == 'q')break;result = exp();if (token == '\n')printf("Result is: %g\n", result);elseerror();}return 0;}double exp(void){double temp = term();while (token == '+' || token == '-')switch(token){case '+': match('+');  temp += term();  break;case '-': match('-');  temp -= term();  break;}return temp;}double term(void){double temp = factor();while (token == '*' || token == '/')switch(token){case '*': match('*');  temp *= factor();  break;case '/': match('/');  temp /= factor();  break;}return temp;}double factor(void){double temp;if (token == '('){match('(');temp = exp();match(')');} else if (isdigit(token)){ungetc(token, stdin);scanf("%lf", &temp);token = getPrintableChar();} elseerror();return temp;}void error(void){fprintf(stderr, "Error!\n");exit(EXIT_FAILURE);}void match(char expectedToken){if (expectedToken == token)token = getPrintableChar();elseerror();}char getPrintableChar(void){char temp;dotemp = getchar();while (isblank(temp));return temp;}

The program implementation logic is implemented according to the EBNF rules, namely:

<exp> -> <term> { <addop> <term> }<addop> -> + | -<term> -> <factor> { <mulop> <factor> }<mulop> -> * | /<factor> -> ( <exp> ) | Number

We will not go into details about EBNF here.

How to use C language to implement a simple calculator

# Include <stdio. h>
# Include <stdlib. h>
# Include <string. h>
Int main ()
{
Char s [101], x [101], y [101], * t, op;
Gets (s );
Int I, j, n = strlen (s );
Double a, B;
For (I = j = 0; s [I]! = ''; I ++)
X [j ++] = s [I];
X [j] = 0;
A = strtodd (x, & t );
I ++;
For (j = 0; I <n; I ++)
{
If (j = 0)
{Op = s [I ++];
I ++;
}
Y [j ++] = s [I];
If (s [I] = '')
{
Y [j] = 0;
B = strtodd (y, & t );
J = 0;

}
If (j = 0)
Switch (op)
{
Case '+': a + = B; break;
Case '-': a-= B; break;
Case '*': a * = B; break;
Case '/': a/= B; break;
};
}
Printf ("% f \ n", );
}

Implement a simple arithmetic calculator by using C language programming

# Include <stdio. h>

// Function, read Operations
Int getNextNum ()
{
Int ret;
Scanf ("% d", & ret );
Return ret;
}

// Function, read Operator
Char getOpt ()
{
Return getchar ();
}

// Function, computing
Int caculate (int op1, int op2, char opt)
{
If (opt = '+') return op1 + op2;
If (opt = '-') return op1-op2;
If (opt = '*') return op1 * op2;
If (opt = '/') return op1/op2;
Return 0;
}

Int main ()
{
Int op1, op2;
Char opt;
// Place the calculation result in the first operand
Op1 = getNextNum ();
While (1)
{
Opt = getOpt ();
If (opt = ') break;
Op2 = getNextNum ();
Op1 = caculate (op1, op2, opt );
}
Printf ("% d \ n", op1 );
}
Return 0;
}