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lab9(postfix_eval).c
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#include<stdio.h>
#include<ctype.h>
int stack[20];
int top = -1;
void push(int x){
stack[++top] = x;
}
int pop(){
return stack[top--];
}
void main(){
char exp[20];
int n1,n2,n3,num;
printf("Enter the expression :: ");
scanf("%s",exp);
int i=0;
while(exp[i] != '\0') {
if(isdigit(exp[i]))
{
num = exp[i] - '0';
// or
//num = exp[i] - 48 ;
// this can be done so as to convert the individual char numbers to the respective numerical values
push(num);
}
else
{
n1 = pop();
n2 = pop();
switch(exp[i])
{
case '+':
{
n3 = n1 + n2;
break;
}
case '-':
{
n3 = n2 - n1;
break;
}
case '*':
{
n3 = n1 * n2;
break;
}
case '/':
{
n3 = n2 / n1;
break;
}
}
push(n3);
}
i++;
}
printf("\nThe result of expression %s = %d\n\n",exp,pop());
}