java - Convert for loop into a recursive function -

this homework problem. i'm having trouble converting following recursive function:

public class integrate {     public static double integrate(int  a, int b, int steps)     {         double sum=0;         double delta = 1.0 * (b - a)/steps;         double x = a;         double f = 0.5*x*x + 3*x + 5;          (int = 0; i< steps; i++)         {             x = x + delta;             double fr = 0.5*x*x + 3*x + 5;             double area = f * delta + 0.5*(fr - f)*delta;             sum += area;             f = fr;         }         return sum;     }     public static void main(string [] args)     {         int a, b, step;         = integer.parseint(args[0]);         b = integer.parseint(args[1]);         step = integer.parseint(args[2]);         system.out.format("integral %f\n", integrate(a,b,step));     } } 

this have far output not same original code. can't figure out wrong

public class integrate {      public static double integrate(int a, int b, int steps) {         double sum=0;         int i=0;         sum = rintegrate(a, b, steps, i, sum);         return sum;     }      public static double rintegrate(int a, int b, int steps,              int i, double sum) {         double delta = 1.0 * (b - a)/steps;         double x = a;         double f = 0.5*x*x + 3*x + 5;         if (i<steps) {             x = x + delta;             double fr = 0.5*x*x + 3*x + 5;             double area = f * delta + 0.5*(fr - f)*delta;             sum += area;             f = fr;             i++;             rintegrate(a, b, steps, i, sum);         }         return sum;     }      public static void main(string[] args) {         int a, b, step;         = integer.parseint(args[0]);         b = integer.parseint(args[1]);         step = integer.parseint(args[2]);         system.out.format("integral %f\n", integrate(a,b,step));     }  } 

i'm not going analyze problem, here observations have

    if (i<steps) {         x = x + delta;         double fr = 0.5*x*x + 3*x + 5;         double area = f * delta + 0.5*(fr - f)*delta;         sum += area;         f = fr;         i++;         rintegrate(a, b, steps, i, sum);     }     return sum; 

everything between sum += area; , return sum; superfluous.

• you're setting f fr, never use f after that. if want f different next time, maybe can pass parameter recursive function
• you're recursively calling rintegrate(...), you're not doing value returns. might want use value.

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you should think recursion using smaller version of problem solve itself.

here's code problem assuming have function: segment calculates size of first segment given a, , delta

rintegrate(a, b, steps) {     if(steps <= 1)     {         delta = b-a;         return segment(a, delta)     }     else     {         delta = (b-a)/steps         return segment(a, delta) + rintegrate(a+delta, b, steps-1)     } }