Question

(Using C++) Create a function that will solve integer postfix equations. (must implement own stack, can’t use std::stack )

Answer 1

#include <iostream>
#include <stdio.h>

#include <string.h>

char stack[100];   
int top = -1;

void printArray(int array[], int size) {
int i;
for ( i = 0; i < size; i++)
{
printf("%d,", array[i]);
}
printf("\n");
}

int isempty() {

if(top == -1)
return 1;
else
return 0;
}
  
int isfull() {

if(top == 99)
return 1;
else
return 0;
}

int peek() {
return stack[top];
}

int pop() {
int data;

if(!isempty()) {
data = stack[top];
top = top - 1;  
return data;
}else {
printf("Could not retrieve data, Stack is empty.\n");
}
}

int push(int data) {

if(!isfull()) {
top = top + 1;  
printf("push %d, top is %d\n", data, top);
stack[top] = data;
//printf("push stack[top] = data, top is %d\n", top);
}else {
printf("Could not insert data, Stack is full, top is %d.\n", top);
}
}
int eval(int op1, int op2, char operate) {
switch (operate) {
case '*': return op2 * op1;
case '/': return op2 / op1;
case '+': return op2 + op1;
case '-': return op2 - op1;
default : return 0;
}
}
int processexpr(char expr[])
{
// write this function
int i = 0;
char ch;
int val;
int size = strlen(expr);
while (expr[i]!='\0') {
ch = expr[i];
if(ch=='=')
return val;
if (isdigit(ch)) {
push(ch-'0');
}
else {
int op1 = peek();
pop();
int op2 = peek();
pop();
val = eval(op1, op2, ch);
push(val);
}
i++;
}
return val;

}

int main() {

char expr[100] = "31+=";
int x = processexpr(expr);
printf("%s %d\n", expr, x);

// make your own postfix expression to test
// and print out the result
}
===================================
See Output


saved share run gcc version 4.6.3 push 3, top is 0 push 1, top is1 push 4, top is 0 31+- 4 main.cpp 67 68 69 70 case '-': return op2 - op1; default return 0 71 int processexpr(char expr[) 72 73 I write this function 74 int i-0; 75 76 char ch; int val; int size- strlen (expr); 78 while (expr[i]!-'0) ch expr[i]; if (ch-'-' return val; if (isdigit(ch)) 79 80 81 82 83 84 85 86 87 push(ch-'0'); else f int op1 peek); pop ); int op2peek); pop ); val eval (op1, op2, ch); push(val); 89 90 91 92 93 94 95 96 97 98 return val; 99 int main 100 101 102 103 104 char expr [100] "31+" int xprocessexpr(expr); printf("%s %d\n", expr, x); 105 I/ make your own postfix expression to test 106 // and print out the result 107

Thanks