Writing to a file

/* write_file.c */

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

# define Pi M_PI


int main()
{
int i;
FILE *fp;

fp = fopen("output.txt","w");
     fprintf(fp, " Angle \t Sine \n");
    fprintf(fp, "--------------------------\n");
for (i = 0;i <= 90;i++)
    fprintf(fp,"%2d \t %f\n",i,sin((i/90.0)*(Pi/2)));

fclose(fp);
}

Powers of 2

#include <stdio.h>

unsigned long power2(int exp) {

 unsigned  long res;

    if (exp == 0)
      res = 1;             /* Zeroth power is equal to 1 */
    else
      res = 2 * power2(exp-1); /* Recursive definition of power2 */
    return(res);
}

int main() {

    int m, n;

    printf("Enter a positive integer > ");
    scanf("%d",&n);
for(m = 1; m <= n; m=m+1 )
    printf("%2d power of 2 is equal to %12lu.\n",m, power2(m));
}

Factorial

#include <stdio.h>

int fact(int n) {

    int res;

    if (n == 0)
      res = 1;             /* Factorial of 1 is equal to 1 */
    else
      res = n * fact(n-1); /* Recursive definition of factorial of n */
    return(res);
}

int main() {

    int n; 

   printf("Enter a positive integer > ");
   scanf("%d",&n);
   printf("%d factorial is equal to %d.\n",n, fact(n));
}