Why is this program not working for power with negative numbers?

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>

int evaluate(char p[],int size, int num1);
void read_values();
void calc();
int values[100];
int i,temp,num,j,k,l=0,result=0,temp_position=0,values_size=0;
char p1[100],arr_temp[100],a[100];

int main(){
	scanf("%s",p1);
	read_values();
	calc();
	values[values_size]=evaluate(p1,100, values[values_size]);
	printf("%s\n",p1);
	for(j=0;j<values_size;j++)
	{
		printf("%d\n",values[j]);
	}
	return 0;//end of main
}
void read_values(){	
	do
	{
		scanf("%d",&temp);
		if(temp==1000)
			break;
		else
		{
			values[values_size]=temp;
			values_size++;
		}
	}
	while(values[values_size]!=1000);
}	

void calc(){
	k=0;
	for(l=0;p1[l]!='\0';l++)
	{	
		if((p1[l]=='('))//opening bracket encountered
		{	temp_position=0;
			while(p1[++l]!=')')
			{
				a[temp_position++]=p1[l];
			}
			arr_temp[k++]=evaluate(a,temp_position,values[values_size])+48;
		}
		else 
			arr_temp[k++]=p1[l];//copy directly until opening bracket		
	}
	values[values_size]=evaluate(arr_temp,100, values[values_size]);
	values_size++;
}

int evaluate(char p[],int size, int num1){
	for(i=0;p[i+1]!='\0';i++)
	{
		if(i==0)
		{
			if(p[0]>='a'&&p[0]<='z')
				result = num1;
			else
				result =p[0]-48;
		}
		if (p[i]=='^')
		{
			if(p[i+1]>='a'&&p[i+1]<='z')
				result=pow(result,num1);
			else
				result=pow(result,(p[i+1]-48));
		}
	}
	return result;
}