powers of two, recursion.

[Alfy]

int ans, guess, random, type, counter, num, i;
char option[20], numb[10], input[5];


int power(int num)
{
    ans=2;
    if(num==0)
    {
        return(1);
    }    
    if(num<0)
    {
        printf("incorrect input, please input a positive integer:");
        return(0);
    }    
    
    else
        for(i=1; i!=num; i++)
            {
                    return(ans=ans*2);
            }    
    return(0);
} 

int main()
{
/*before this there is all the switch case stuff*/
case 1 : 
     	/*powers of 2 calculator*/
printf("please enter a positive integer:\n");
fgets(numb, sizeof(numb), stdin);
sscanf(numb, "%d",&num);
printf("the answer is:%d\n",power(num));
break;

ok so the origional was:
case 1 : 
				/*powers of 2 calculator*/
			printf("please enter a positive integer:\n");
            fgets(numb, sizeof(numb), stdin);
            sscanf(numb, "%d", &num);
            ans=2;
            if(num<0)
            printf("incorrect input, please input a positive integer:");
            if(num==0)
            printf("the answer is 1\n");
            for(i=1; i!=num; i++)
            ans=ans*2;
            printf("The answer is %d\n", ans);
			break;

and i had to take that and turn it into a recursive function. IDK what recursion is other than "it calls itself" or something... anyway im lost on this.
please help!

[kunal_ktr]

here is the recursive code for calculating power of 2;
int power(int num)
{
if(num==0)
return 1;
if(num==1)
return 2;
return 2*power(num-1);
}

well after including this function in ur prog, u dont need to check whether the input value is 0 or 1. but check for -ve entry..

here is ur modified switch statements ...
case 1 :
/*powers of 2 calculator*/
printf("please enter a positive integer:\n");
fgets(numb, sizeof(numb), stdin);
sscanf(numb, "%d", &num);
//ans=2;
if(num<0)
printf("incorrect input, please input a positive integer:");
else{
ans=power(num);
printf("The answer is %d\n", ans);}
break;