Exponential function with addition

I am trying to create exponential function with for loop. so if num1 is 10, and num2 is 2

for (i = 0; i < num1; i++)
      sum = sum + num2;
for (i = 开发者_JAVA百科0; i < num2 ; i++)
      sum2 = sum + sum2;

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Repeated addition mimics multiplication.
Repeated multiplication mimics exponentiation.

Just make two loops, one inside another: the inner loop to mimic multiplication and the outer loop to mimic exponentioation.

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EDIT: here's a recursive method. Transforming it into a couple loops shouldn't be too difficult. Tested on codepad.

#include <stdio.h>

int mul(int b, int e) {
  if (e == 0) return 0;
  if (e == 1) return b;
  return b + mul(b, e - 1); /* additions only */
}

int expo(int b, int e) {
  if (e == 0) return 1;
  if (e == 1) return b;
  return mul(b, expo(b, e-1));
}

int main(void) {
  printf("3^0 is %d\n", expo(3, 0));
  printf("3^1 is %d\n", expo(3, 1));
  printf("3^2 is %d\n", expo(3, 2));
  printf("3^3 is %d\n", expo(3, 3));
  printf("3^4 is %d\n", expo(3, 4));
  return 0;
}

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If you don't like me using /, implement your FPU yourself.

Something like this?

double power(int x, int p){
    if(p==0)
        return 1.0;

    double res = x;
    for(int i=1 ; i<p ; ++i)
        res += x;

    return res;
}

long mul(long a, long b){
    if(a==0 || b==0)
        return 0;

    long res = 0;
    for(int i=0 ; i<a ; ++i){
        res += b;
    }
    return res;
}

long fac(long x){
    if(x==0)
        return 1;
    return mul(fac(x-1),x);
}

double exponential(int x, int c) 
{
    double res = 0.0;
    for(int i=0; i<=c;++i)
        res += power(x)/(double)fac(i);
    return res;
}

Not tested, see http://en.wikipedia.org/wiki/Exponential_function for definition of formula.