..................の間がプログラム本体です

program 1
..................
#include<stdio.h>
/* 実数の足し算 */
main()
{
  float x;
  x = 10.0;
  printf("x= %f\n",x);
  x += 5.0;
  printf("x= %f\n",x);
}
..................
program 2
..................
#include<stdio.h>
/* 整数の足し算 */
main()
{
  int i;
  i = 10;
  printf("i= %d\n",i);
  i += 5;
  printf("i= %d\n",i);
}
...................
program 3
...................
#include<stdio.h>
/* 足し算のくりかえし */
main()
{
  float x1,x2;                        
  int i;                               
  x1 = 0.0;
  x2 = 0.0;
  for( i=1; i<=10; ++i){
    x1 += 5.0;
    x2 += i*5.0;
    printf("i= %d  x1= %f  x2= %f\n",i,x1,x2);
   }
}