Write a C Program to fine the Compound Interest

/*Using pow function*/
#include<stdio.h>
#include<math.h>
void main()
{
     float p,r,i,t,ci,a;

     printf("Amount : ");
     scanf("%f",&p);
     printf("Interest rate %: ");
     scanf("%f",&r);
     printf("Type the period in years: ");
     scanf("%f",&t);

     i=1+(r/100);

     ci=pow(i,t);
   
     ci=p*ci-p;

     printf("Compounded interest is : %.2f",ci);

}



/*Using for loop*/
#include<stdio.h>

void main()
{
     float p,r,i,t,ci,a;


     printf("Amount : ");
     scanf("%f",&p);
     printf("Interest rate %: ");
     scanf("%f",&r);
     printf("Type the period in years: ");
     scanf("%f",&t);

     i=1+(r/100);

     ci=1;
     for(a=1;a<=t;a++)
        ci=ci*i;

     ci=p*ci-p;

     printf("Compounded interest is : %.2f",ci);

}


/* Checking Invalid Input */
#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
 float p,t,r;
 float i,compound,a;
 clrscr();

 printf("enter principal:\t");
 scanf("%d",&p);

 printf("enter rate of interest:\t");
 scanf("%d",&r);

 printf("enter time in years:\t");
 scanf("%d",&t);

 if((p<1)||(t<1)||(r<1))
  printf("invalid");
 else
 {
  a=(float)p*(pow(1+r/100.0,t));
  compound=a-p;
  printf("the compound interest is rs.%.2f",compound);
 }
 getch();
}