계산기 (후위표현식)

후위 표현식을 이용한 계산기 작성

int postfix( const char * expression ) ///////////후위표기법

{

char stack[MAX_STACK] = {0,};

char stack_post[MAX_STACK] = {0,};

int i=0, Count=0, Top=0;

printf("token : stack \n", expression[i]);

for( ; i < strlen(expression) ; i++)

{

printf("  %c   : ", expression[i]);

if(expression[i]>='0' && expression[i]<='9')

{

if(expression[i+1] == '+' || expression[i+1] == '-' || expression[i+1] == '*' || 

   expression[i+1] == '/' || expression[i+1] == ')' || expression[i+1] == '\0')

{

stack_post[Count++] = expression[i];

stack_post[Count++] = ' '; // ' ' 삽입(숫자알아보기위해)

}

else

{

stack_post[Count++] = expression[i];

}

} 

else if( expression[i]=='+' || expression[i]=='-' )

{

if( stack[Top-1]=='*' || stack[Top-1]=='/' || stack[Top-1]=='+' || stack[Top-1]=='-' )

{

stack_post[Count++] = stack[--Top];

stack[Top++] = expression[i];

}

else

{

stack[Top++] = expression[i];

}

}

else if(expression[i]=='*'|| expression[i]=='/')

{

if( stack[Top-1]=='*' || stack[Top-1]=='/' )

{

stack_post[Count++] = stack[--Top];

stack[Top++] = expression[i];

}

else

{

stack[Top++] = expression[i];

}

}

else if(expression[i]==')')

{

while(1)

{

if(stack[--Top] == '(')

{

stack[Top]=0; break; 

}

stack_post[Count++] = stack[Top];

stack[Top]=0;

}

}

else

{

stack[Top++] = expression[i];

}

printf("%s \n", stack);

}

while(Top!=0)

{

stack_post[Count++] = stack[--Top];

stack[Top]=0;

}

printf("stack_post notation : %s \n", stack_post);

return calculate( stack_post );

}

int calculate( const char * expression)

{

int len = strlen(expression);

int i = 0, count = 0;

int result[MAX_STACK] = {0,};

for( ; i < len ; i++)

{

if( expression[i]>='0' && expression[i]<='9' && expression [i] != ' ' )

{

result[count]  += expression[i] - '0';

if( expression[i + 1] != ' ' )

{

result[count] *= 10;

}

}

else if(expression [i] == ' ' )

{

count++;

}

else

{

switch(expression[i])

{

case '+':

{

count --;

result[count - 1] = result[count - 1] + result[count];

result[count] = 0;

}break;

case '-':

{

count --;

result[count - 1] = result[count - 1] - result[count];

result[count] = 0;

}break;

case '*':

{

count--;

result[count - 1] = result[count - 1] * result[count];

result[count] = 0;

}break;

case '/':

{

count--;

result[count - 1] = result[count - 1] / result[count];

result[count] = 0;

}break;

}

}

}

return result[0];

}