C Program for Evaluation of Postfix Expression

C Program for Evaluation of Postfix ExpressionIn this program we evaluate the Postfix Expression, using the stack. For example, 456*+7- is the postfix expression, from left one by one it is inserted into the stack, and after evaluation the answer is 27. Read more about C Programming Language .

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#define SIZE 50 /* Size of Stack */
#include <ctype.h>
int s[SIZE];
int top=-1; /* Global declarations */

push(int elem)
{ /* Function for PUSH operation */
s[++top]=elem;
}

int pop()
{ /* Function for POP operation */
return(s[top--]);
}

main()
{ /* Main Program */
char pofx[50],ch;
int i=0,op1,op2;
printf("nnRead the Postfix Expression ? ");
scanf("%s",pofx);
while( (ch=pofx[i++]) != '')
{
if(isdigit(ch)) push(ch-'0'); /* Push the operand */
else
{ /* Operator,pop two operands */
op2=pop();
op1=pop();
switch(ch)
{
case '+':push(op1+op2);break;
case '-':push(op1-op2);break;
case '*':push(op1*op2);break;
case '/':push(op1/op2);break;
}
}
}
printf("n Given Postfix Expn: %sn",pofx);
printf("n Result after Evaluation: %dn",s[top]);
}
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