function problem

[stablex]

have a problem, when int n=1 float a and b variable's are still the same when n=0. i write this program without function it work.

float people(float firstyear, float grow){
    float total;
    grow = firstyear / 100 * 4.5;
    firstyear= grow + firstyear;
    total=firstyear;
    return total;
}

int main()
{
    float a = 65, b = 0;
    int n;

    for(n = 0; n < 5; n++){
    printf("%.2f\n", people(a ,b));
    }
    return 0;
}

without function

int main()
{
    float firstyear=650000, grow=0;
    int n;

    for(n = 0; n < 5; n++){

    grow = firstyear / 100 * 4.5;
    firstyear= grow + firstyear;

    printf("%.2f\n", firstyear);
    }
    return 0;
}

[jimblumberg]

In your first program you never change the values of a or b so the return value from the function will never change. In your second program you do actually change your variables each time thru your loop. If you run the program through your debugger, after putting in a breakpoint you should be able to single step through both programs and see the differences in your variables.


Jim

[AndiPersti]

The changes you've made to "grow" and "firstyear" inside your function are only visible within the function body (local scope). As soon as you return to main() all these changes are lost. Thus "a" and "b" in main() will never change.

Bye, Andreas

[std10093]

In other words,you need to pass a reference of these two variables in order the modifications made to them will be remember after the termination of the function

[stablex]

In your first program you never change the values of a or b so the return value from the function will never change. In your second program you do actually change your variables each time thru your loop. If you run the program through your debugger, after putting in a breakpoint you should be able to single step through both programs and see the differences in your variables.


Jim

yeah, how can i change float variable a and b during my for loops?

[stablex]

In other words,you need to pass a reference of these two variables in order the modifications made to them will be remember after the termination of the function

pass a reference is using pointer?

[std10093]

yeah, how can i change float variable a and b during my for loops?

See the post i made 1 min ago

Remember this

void modificationsRemain(int *a,int *b)
{
          *a=500;/*random numbers*/
          *b=6000;
}

void modificationsNotRemain(int a ,int b)
{
        a=5554543;
        b=5664;
}

int main(void)
{   
         int a=5;
         int b=3;
         printf("a= %d and b= %d \n",a,b);
         modificationsNotRemain(a,b);
         printf("a= %d and b= %d \n",a,b);
         modificationsRemain(&a,&b);
         printf("a= %d and b= %d \n",a,b);
         return 0;
}

[std10093]

pass a reference is using pointer?

Exactly

[stablex]

but book exercise tell me need to use Call by Value. it that possible?

[jimblumberg]

Yes it is possible, but you will need to return the value from your function to a variable that changes the variable you pass to your function. Also you really only need to pass one variable into your function.

Jim

[stablex]

Yes it is possible, but you will need to return the value from your function to a variable that changes the variable you pass to your function. Also you really only need to pass one variable into your function.

Jim

do you have example code? because i dont really get it.

[jimblumberg]

Here is one way of changing the value of a variable in main.

#include <stdio.h>

int modifyInt(int value)
{
   value += 10;
   return(value);
}

int main(void)
{
   int number = 0;
   int i;
   for( i = 0; i < 5; ++i)
   {
      number = modifyInt(number);
      printf("The number is now: %d\n", number);
   }
}

Jim