below is my entire code...i cant think of how to change one part in double calArray(char* formula) to something else instead of using string.h.....could someone please help!!! i'm totally lost!!
if user input 1+2+4-3*5
output is 20
#include <stdio.h>
#include <stdlib.h>
#include "arithCalculation.h"
#define TRUE 1
#define FALSE 0
void mainarithCalculation()
{
char formula[70];
printf("\n **********************************************************************\n"

;
printf("\n\t\tWELCOME to Task 1: Basic Arithmetic Calculation \n"

;
printf("\n **********************************************************************\n"

;
while(TRUE)
{
/* get user input */
printf("\n\nPlease enter a formula:"

;
fgets(formula, 70, stdin);
printf("Input: \t%s ", formula);
/* if input is over maximum length*/
if (length(formula)>70)
{
printf("\nEquation length is more then 70!"

;
continue;
}
/* if input is lesser then 3 in length*/
else if (length(formula)<3)
{
printf("\nEquation must have two numbers and an operator!"

;
continue;
}
/* if input does not contain at least 2 values and operator and doesn't end with an operator */
else if (checkInput(formula))
{
printf("\nInvalid input!"

;
continue;
}
else
{
returnResult(formula);
clrscr();
break;
}
}
}
/*check for errors
Operators will not be the last and first
There must be at least two numbers*/
int checkInput(char* formula)
{
char one, two;
int i;
/*check if first character is a operator*/
if (checkValidOperator(formula[0]))
{
return FALSE;
}
/*checks for operator errors*/
for(i = 1; i< length(formula); i++)
{
one = formula[i-1];
two = formula
;
if (checkValidOperator(one) && checkValidOperator(two))
{
return FALSE;
}
}
/*check for valid characters*/
for (i = 0; i< length(formula); i++)
{
if(!checkValidNumber(formula) && !checkValidOperator(formula))
{
return FALSE;
}
}
/*check if last character is a operator*/
if(checkValidOperator(formula))
{
return FALSE;
}
return TRUE;
}
/*check if input is integer*/
int checkValidNumber(char valid)
{
switch(valid)
{
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '0':
return TRUE;
default:
return FALSE;
}
}
int checkValidOperator(char op)
{
switch(op)
{
case '+':
case '-':
case '*':
case '/':
return TRUE;
default:
return FALSE;
}
}
/*check length of input and returns the length*/
int length(char* formula)
{
int i;
for(i = 0; formula!= '\0'; i++)
{
/* no code */
}
return i;
}
/*calculate the input formula*/
double calArray(char* formula)
{
double num1, num2;
char numString[70][20];
int lastOp = 0;
int i = 0;
int j = 0;
double result;
/*************do this without using string.h************/
for(i = 1; i < length(formula); i++)
{
if(checkValidOperator(formula)
{
/*strcpy(numstring[j], portion of formula - 1);
j++;
i++;
lastOp = i;
*/
}
}
/* strcpy(numstring[j], last part of formula);*/
/*********************************************************/
/* first number */
result = numstring[0];
/* calculate everything */
for(i = 0; i <= j-2; i+=2)
{
result = cal(result, atod(numstring[i+2]), numstring[i+1][0]);
}
return result;
}
double cal(double num1, double num2, char op)
{
double result;
switch(op)
{
case '+':
result = (num1 + num2);
break;
case '-':
result = (num1 - num2);
break;
case '*':
result = (num1 * num2);
break;
case '/':
if (num2 != 0)
{
result = (num1 / num2);
}
else
{
printf("Divide by 0 error!"
;
exit(EXIT_FAILURE);
}
default :
printf("Illegal operator!"
;
exit(EXIT_FAILURE);
}
return result;
}
/*to return result and print out*/
void returnResult(char* formula)
{
printf("\nResult: \t%6.2lf", calArray(formula));
}
void clrscr()
{
system("cls"
;
}
/*start of program*/
void mainarithCalculation();
/*get result and return to main*/
void returnResult(char* formula);
/*check is user enter correct input*/
int checkInput(char* formula);
/*check if user entered an integer*/
int checkValidNumber(char valid);
/*check if user entered an operator*/
int checkValidOperator(char op);
/*check the length of the input*/
int length(char* formula);
/*calculate the input formula*/
double calArray(char* numString);
double cal(double num1, double num2, char op);
/*clear screen*/
void clrscr();