Thread: For loop doesn't work for positive integers -- while loop works fine.

Code:

#include<stdio.h>

Code:

#include<stdlib.h>


int sumFor(int daNumba);
int sumWhile(int daNumba);


        /*      Main function           */


int main()
{
        /*      Declare variables       */


   int daNumba, startNumba, ansFor, ansWhile;


        /*      Display welcome message         */


   printf("\nWelcome to sumTimes2.\n");


        /*      Message indicating what the program will do     */


   printf("\nThis program will sum the integers between the one you enter and\n");
   printf("the integer that is twice that value.\n");


        /*      Ask the user to enter and receive an integer      */


   printf("\nPlease enter your integer: ", daNumba);
   scanf("%d", &daNumba);


        /*      sumFor program      */


   int sumFor(int daNumba)
   {
     int ansFor=0, startNumba=daNumba;
     for( ; startNumba <= (daNumba*2); )
     {
        ansFor += startNumba++;
     }
     for( ; startNumba >= (daNumba*2); )
     {
        ansFor += startNumba--;
     }
        return ansFor;
   }


        /*      sumWhile program        */


   int sumWhile(int daNumba)
   {
     int ansWhile=0, startNumba=daNumba;
     while(daNumba >0 && startNumba <= (daNumba*2))
     {
        ansWhile += startNumba++;
     }
     while(daNumba <= 0 && startNumba >= (daNumba*2))
     {
        ansWhile += startNumba--;
     }
        return ansWhile;
   }


        /*      Display test statistics         */
   printf("\nFor says the sum is %d\n", sumFor(daNumba));
   printf("While says the sum is %d\n", sumWhile(daNumba));


        /*      Display ending thank you message        */


   printf("\nThank you for using sumTimes2. Bye!\n\n");


        /*      Rieturn 0 for the compiler       */


   return 0;


}

In sumFor, BOTH of the for loops run no matter what the input is, so you need some code logic which ensures only one runs - which one dependant on the sign of the input integer.