Solution
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 50
struct Stack
{
int top;
unsigned capacity;
int* array;
};
struct Stack* createStack( unsigned capacity )
{
struct Stack* stack = (struct Stack*)
malloc(sizeof(struct Stack));
if (!stack)
return NULL;
stack->top = -1;
stack->capacity = capacity;
stack->array = (int*) malloc(stack->capacity *
sizeof(int));
return stack;
}
int isEmpty(struct Stack* stack)
{
return stack->top == -1 ;
}
char peek(struct Stack* stack)
{
return stack->array[stack->top];
}
char pop(struct Stack* stack)
{
if (!isEmpty(stack))
return stack->array[stack->top--] ;
return '$';
}
void push(struct Stack* stack, char op)
{
stack->array[++stack->top] = op;
}
int isOperand(char ch)
{
return (ch >= 'a' && ch <= 'z') ||
(ch >= 'A' && ch <= 'Z');
}
int Prec(char ch)
{
switch (ch)
{
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
case '^':
return 3;
}
return -1;
}
int infixToPostfix(char* exp)
{
int i, k;
struct Stack* stack = createStack(strlen(exp));
if(!stack)
return -1 ;
for (i = 0, k = -1; exp[i]; ++i)
{
if (isOperand(exp[i]))
exp[++k] = exp[i];
else if (exp[i] == '(')
push(stack, exp[i]);
else if (exp[i] == ')')
{
while (!isEmpty(stack) && peek(stack) != '(')
exp[++k] = pop(stack);
if (!isEmpty(stack) && peek(stack) != '(')
return -1;
else
pop(stack);
}
else
{
while (!isEmpty(stack) &&
Prec(exp[i]) <= Prec(peek(stack)))
exp[++k] = pop(stack);
push(stack, exp[i]);
}
}
while (!isEmpty(stack))
exp[++k] = pop(stack );
exp[++k] = '\0';
printf( "%s", exp );
}
int main()
{
char exp[MAX] ;
printf("ENter the EXpression\n");
scanf("%s",exp);
infixToPostfix(exp);
return 0;
}
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