see this:-
Code:
//This program generates a table for the specific internal energy
//and the specific enthalpy of Methane from 300K to 1000K using the
//specific heat variations listed on Table A.21

#include <stdio.h>
#include <conio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

int main(){
  int QA;
  float T1=300,T2,end1,inc;
  double a=3.826,b=-3.979,c=24.558,d=-22.733,e=6.963;
  double A,B,C,D,E,H,U,R=8.3143,M=16.04,i=10;
  char error[128];
  
  do{
  do{
    system("cls");
    printf("Enter the Increment in Temperature: ");
    scanf("%s",&error);
    inc=atof(error);
    if(inc<=0){
      system("cls");
      printf("Invalid Input. Please try again!!!\n");
      printf("Please press the spacebar to continue!!");
      getche();
      }
    }while(inc<=0);
  T2=T1+inc;
  end1=1000-inc;
  printf("The increment is %.3f\n\n",inc);
  printf("\nInitial Temperature\tFinal Temperature\tEnthalpy\tInternal Energy\n");
  while(T1<=end1){
    T1+=inc;
    T2+=inc;
    A=a*(T2-T1);
    B=(1/pow(i,3))*(b/2)*(pow(T2,2)-pow(T1,2));
    C=(1/pow(i,6))*(c/3)*(pow(T2,3)-pow(T1,3));
    D=(1/pow(i,9))*(d/4)*(pow(T2,4)-pow(T1,4));
    E=(1/pow(i,12))*(e/5)*(pow(T2,5)-pow(T1,5));
    H=(R/M)*(A+B+C+D+E);
    U=(R/M)*((A+B+C+D+E)-(T2-T1));
    printf("%10.3f K\t\t%10.3f K\t\t%.3f kJ/kg\t%.3f kJ/kg\n",T1,T2,H,U);
    }
  do{//This used to ask the user if s/he wants to repeat the evaluation
    printf("\n\nDo you want to repeat the computation or Quit?\n");
    printf("[1] Yes\n");
    printf("[2] Quit\n");
    scanf("%s",&error);
    QA=atoi(error);
    switch(QA){
      case 1:
        break;
      case 2://Return to the selection screen
        exit(1);
        break;
      default://The program redirects invalid inputs to this part
        system("cls");
        printf("Invalid input. Please try again!!!\n");
        printf("Please press the spacebar to continue!!");
        getche();
        break;   
        }
      }while(QA>2||QA<1);
    }while(QA==1 && T2<=1000);         
  getche();
}