Question

This code in c evaluates a mathematical expression and checks that it is correctly balanced, then converts the expression to its postfix form (This part works). Now I need to evaluate the postfix expression with a function. I've been compiling it using dev c ++.

#include
#include
#define SIZE 20
#include
int profundidad(char expresion[]);
int prec(char op1, char op2);
void postfijo(char expresion[]);
char funcion[SIZE];
float convierte(char car);
float resultado(float opnd1, char symb, float opnd2);
float evaluar(char expresion[]);
#define SIZE 20

char dato;

struct Nodo
{
char info;
struct Nodo* sig;
};

typedef struct Nodo nodo;
nodo* raiz = NULL;

int isEmpty()
{
if (raiz == NULL)
return 1;
else
return 0;
}

void push(char dato)
{
nodo* nuevo = NULL;
if (isEmpty())
{
nodo* nuevo = NULL;
nuevo = (nodo*)malloc(sizeof(nodo));
nuevo->info = dato;
nuevo->sig = NULL;
raiz = nuevo;
}

else
{
nuevo = (nodo*)malloc(sizeof(nodo));
nuevo->info = dato;
nuevo->sig = raiz;
raiz = nuevo;
}

}

char pop(void) {

nodo* recorre = NULL, * elimina = NULL;
char dato;
if (!isEmpty())
{
elimina = raiz;
dato = elimina->info;
raiz = raiz->sig;
free(elimina);
}
return dato;
}

char stackTop()
{
return raiz->info;
}

void imprimePila()
{
nodo* recorre = raiz;
while (recorre != NULL)
{
printf("%c, ", recorre->info);
recorre = recorre->sig;
}
printf("\n");
}

int main()
{

printf("enter a mathematical expression: \n");
gets(funcion);

if (profundidad(funcion) == 1)
{
printf("the expression is balanced\n");
printf("infix: %s\n", funcion);
postfijo(funcion);
printf("the function evaluated is:%f\n", evaluar(funcion));

}
else
{
printf("the expression is not balanced\n");
}

system("pause");
return 0;

}

int profundidad(char expresion[])
{
char symb, temp;
int i = 0;

while (expresion[i] != '\0')
{
symb = expresion[i];

if (symb == '(' || symb == '[' || symb == '{')
{
push(symb);
}
if (symb == ')' || symb == ']' || symb == '}')
{
if (isEmpty())
{
return 0;
}

else
{
temp = pop();

if (temp == '(')
{
if (symb != ')')
{
return 0;
}
}
else if (temp == '{')
{
if (symb != '}')
{
return 0;
}
}

else if (temp == '[')
{
if (symb != ']')
{
return 0;
}
}
}
}
i++;
}

if (!isEmpty())
{
return 0;
}
else
{
return 1;
}

}

int prec(char op1, char op2) {

int jer1 = 0;
int jer2 = 0;
switch (op1) {

case '(':
jer1 = 0;
break;
case '{':
break;
jer1 = 0;
break;
case '[':
jer1 = 0;
break;
case ')':
jer1 = 3;
break;
case '}':
jer1 = 3;
break;
case ']':
jer1 = 3;
break;
case '^':
jer1 = 3;
break;
case '*':
jer1 = 2;
break;
case '/':
jer1 = 2;
break;
case '+':
jer1 = 1;
break;
case '-':
jer1 = 1;
break;
default:
break;
}
switch (op2)
{
case '(':
jer2 = 3;
break;
case '[':
jer2 = 3;
break;
case '{':
break;
jer2 = 3;
break;
case ')':
jer2 = 1;
break;
case '}':
jer2 = 1;
break;
case ']':
jer2 = 1;
break;
case '^':
jer2 = 3;
break;
case '*':
jer2 = 2;
break;
case '/':
jer2 = 2;
break;
case '+':
jer2 = 1;
break;
case '-':
jer2 = 1;
break;
default:
break;
}
if (jer1 >= jer2)
{
return 1;
}
else
{
return 0;
}
}

void postfijo(char expresion[])
{
int i = 0, j = 0;
char symb = '\0', topsymb = '\0';
char postfijo[SIZE];
while (expresion[i] != '\0')
{
symb = expresion[i];
if ((symb != '+') && (symb != '-') && (symb != '*') && (symb != '/') && (symb != '^') && (symb != '(') && (symb != ')') && (symb != '[') && (symb != ']') && (symb != '{') && (symb != '}'))
{
postfijo[j] = symb;
j++;
}
else
{
while (!isEmpty() && prec(stackTop(), symb))
{
topsymb = pop();
postfijo[j] = topsymb;
j++;
}
if (isEmpty() || (symb != ')' && symb != '}' && symb != ']'))
{
push(symb);
}
else
{
topsymb = pop();
}

}
i++;
}
while (!isEmpty())
{
topsymb = pop();
postfijo[j] = topsymb;
j++;
}

printf("Postfix: %s\n", postfijo);
}

I need to create a function to evaluate the postfix expression

Answer 1

Function To Evaluate Postfix Expression

 struct Stack { int top; unsigned capacity; int* array; }; // Stack Operations 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)); if (!stack->array) return NULL; 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; } // The main function that returns value of a given postfix expression int evaluatePostfix(char* exp) { // Create a stack of capacity equal to expression size struct Stack* stack = createStack(strlen(exp)); int i; // See if stack was created successfully if (!stack) return -1; // Scan all characters one by one for (i = 0; exp[i]; ++i) { // If the scanned character is an operand (number here), // push it to the stack. if (isdigit(exp[i])) push(stack, exp[i] - '0'); // If the scanned character is an operator, pop two // elements from stack apply the operator else { int val1 = pop(stack); int val2 = pop(stack); switch (exp[i]) { case '+': push(stack, val2 + val1); break; case '-': push(stack, val2 - val1); break; case '*': push(stack, val2 * val1); break; case '/': push(stack, val2/val1); break; } } } return pop(stack); } 

Int this Function You will Pass Your Character String to evaluatePostfix and it will return You the evaluated Result.