I'm having problems here with this function i'm making, i need to make function that will write to a text file. This function has to ask the user for the file name and check if it exists. If this is all good then it will write the string in the buffer to the text file. The string is no bigger than 60chars.
so far i have started it but i am having diffuculty in understanding it, my text book isn't the best help either. Below is my function so far

void write_string(File *fp, char *s)
{
File *ptr;
int i;

ptr == fopen(fp, "w");
if (ptr == NULL)

}

My problem is what is fp, its coming from the main but what is it exactly?
Here is my code for the whole program please view if it makes more sense..Please i need some help

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <conio.h>
#include <string.h>
#include <iostream.h>


//void instruct(void);
//void classify(char cInput[], float fstats[], int i, int iOdd, int iEven, int iUpper,
		  // 	 int iLower, int iOaverage, int iEaverage);
void instruct(char *cInput);
void summary(float fstats[], int i, int iOdd, int iEven, int iUpper,
			 int iLower, int iOaverage, int iEaverage);
//int  count(char cChoice, char cInput[]);
int  search(char cGet, char cInput[]);
void menu(void);
int modify ( const char x, const char y, char *s);
void classify(char *cInput, float *fstats);
int count(char cChoice, char *cInput);
void write_string(File *fp, char *s)

void main(void)
{
										
	int iOdd=1, iEven=2;
	int i=0, iCheck=0, j, iChange = 0;
	int iUpper=3, iLower=4;
	int iOaverage =5, iEaverage=6;
	char cInput [61] = {"0"};
	float fstats[7]={0,0,0,0,0,0,0};
	char cPick , cChoice, cGet, cReplace;

	cInput[i]='\0';
	menu();
	cPick = getche();

	for (;cPick != '9'; )
	{
		switch(cPick)
		{
			case '1':  system("cls");
					   cInput[i]='\0';
					   for (j=0; j<=6; j++)
						   fstats[j]=0;
			           instruct(cInput);
			           //classify(cInput,fstats,i,iOdd,iEven,iUpper,iLower,iOaverage,iEaverage);
					   classify(cInput,fstats);
			           break;

	        case '2':  iCheck = strlen(cInput);
			           if (iCheck >=1)
					   {
							system("cls");
				            for (j=0; j<iCheck;j++)
								printf("%c", cInput[j]);
							printf("\n");
					   }
					   else
						   printf("\nThere is no string in the memory please input a string first\n");
					   //cin.clear(); 
					   //cin.ignore(80,'\n'); 
			           //cin.get();
					   system("pause");
			           break;

	        case '5':  iCheck = strlen(cInput);
				       if (iCheck >=1)
					   {
						   system("cls");
					       printf("Please input the character to search:");
					       cGet = getche();
						   if (search(cGet, cInput) > 0)
							   printf("\nthe character occurs first at the index %d\n",search(cGet,cInput));
						   else
							   printf("\nthere are no occurences of that character\n");
					   }
					   else
						   printf("\nThere is no string in the memory please input a string first\n");
					       
					   //cin.get();
					   system("pause");
					   break;

	        case '6':  iCheck = strlen(cInput);
				       if (iCheck >=1)
					   {
						   system("cls");
					       printf("please input character:");
					       cChoice = getche();
						   if (count(cChoice,cInput) >0)
							   printf("\nThere are %d occurences of the character %c\n", count(cChoice, cInput), cChoice);
						   else 
							   printf("\nthere are no occurences of that character\n");
					   }
				       else
						   printf("\nThere is no string in the memory please input a string first\n");
					   //cin.get();
					   system("pause");
				       break;

	        case '8':  iCheck = strlen(cInput);
			           if (iCheck >=1)
					   {
				           system("cls");
				           summary(fstats,i,iOdd,iEven,iUpper,iLower,iOaverage,iEaverage);
					   }
			           else
						   printf("\nThere is no string in the memory please input a string first\n");
					   //cin.get();
					   system("pause");
			           break;

			case '7':  iCheck = strlen(cInput);
			           if (iCheck >=1)
					   {
						   system("cls");
					       printf("character to be replaced:");
					       cChoice = getche();
						   if (count(cChoice,cInput) >0)
						   {
							   printf("\nWith:");
							   cReplace = getche();
							   iChange = modify(cChoice,cReplace,cInput);
							   printf("\nThere have been %d changes made to the string\n", iChange);
							   classify(cInput, fstats);
						   }
						   else
							   printf("\nthere are no occurences of that character\n");
					   }
					   else
						   printf("\nThere is no string in the memory please input a string first\n");
					   system("pause");
			           break;
		}
	system("cls");
	menu();
	cPick = getche();
	}
printf("\n\n");

}

void instruct(char *cInput)
{
	printf("To terminate the program, strike the spacebar or Enter.\n\n\n");
	printf("Next key>");

	int j =0;
	char cTemp;

	cTemp = getche();

	for(;((cTemp != 32) && (cTemp!= 13)); )	//ascii 32 for blank and 13 for carriage return
	{
		if (j <=59)
		{
			if ((cTemp != 8) && (cTemp != 9))
			{
				*cInput = cTemp;
				*(cInput + 1)  = '\0';
				//fstats[i]++;
				j++; 
				cInput = cInput + 1;
			}
			cTemp = getche();
		}
		else 
		{
			printf("\nYou cannot enter more than 60 characters, the first 60 characters will remain\n");
			//printf("hit enter to continue");
			//cin.get();
			system("pause");
			break;
		}
	}



}

void classify(char *cInput ,float *fstats)
{
	int j;
	int iResult =0;
//	int i; 
	float * pstatbeg;
	char * pInputbeg;

	pInputbeg = cInput;
	pstatbeg = fstats;//char cTemp;

	//cTemp = getche();
	for (j=0; j<=6; j++)
		fstats[j]=0;
	//for(;((cTemp != 32) && (cTemp!= 13)); )	//ascii 32 for blank and 13 for carriage return
	for ( ; *cInput !='\0'; cInput = cInput + 1)
	{
		//if ( j<=59)
	//	{
			if (isalpha(*cInput) != 0)
			{
				if (isupper(*cInput) !=0)
					fstats [3]++;
				else
					fstats[4]++;
			}

			if(isdigit(*cInput) !=0)
			{
				if( (*cInput%2) == 0)
				{
					fstats[2]++;
					iResult = *cInput - '0';
					*(fstats +6) = (*(fstats + 6) + iResult);
				}

				else 
				{
					fstats[1]++;
					iResult = *cInput - '0';
					*(fstats + 5) = (*(fstats + 5) + iResult);
				}
			}

			fstats[0]++;
			fstats = pstatbeg;
	}

		 //   if ((cTemp != 8) && (cTemp != 9))
		//	{
		//		cInput[j]= cTemp;
		//		cInput[j+1] = '\0';
		//		fstats[i]++;
		//		j++; 
		//	}
			//	cTemp = getche();
	//	}
	//	else 
	//	{
	//		printf("\nYou cannot enter more than 60 characters, the first 60 characters will remain\n");
			//printf("hit enter to continue");
			//cin.get();
	//		system("pause");
	//		break;
	//	}
	//}// for loop

	if (*(fstats +2) ==0)
		*(fstats +6) = 0;
	else 
		*(fstats + 6) = *(fstats+6)/(*(fstats +2));

	if (*(fstats + 1) ==0)
		*(fstats + 5) =0;
	else
		*(fstats + 5) = *(fstats + 5) /(*(fstats +1));
}

void summary(float fstats[], int i, int iOdd, int iEven, int iUpper,
			 int iLower, int iOaverage, int iEaverage)
{
	system("cls");

	printf("Thank you! Your summary:\n\n");
	printf("Total number of keystrokes entered:%.f\n", fstats[i]);
	printf("Upper case alphabetic characters:%.f\n", fstats[iUpper]);
	printf("Lower case alphabetic characters:%.f\n", fstats[iLower]);
	printf("Even digits:%.f\n", fstats[iEven]);
	printf("Odd digits:%.f\n", fstats[iOdd]);
	printf("Average value of the even digits entered:%.2f\n", fstats[iEaverage]);
	printf("Average value of the odd digits entered:%.2f\n", fstats[iOaverage]);

}

int count(char cChoice, char *cInput)
{
	int i, iNum, iTotal =0;

	iNum = strlen(cInput);
	for ( i=0; i<iNum; i++, cInput = cInput + 1)
	{
		if (cChoice == *cInput)
			iTotal++;
	}

	return iTotal;
}


int search(char cGet, char *cInput)
{
	int i, iIndex=0, iNum=0;

	iNum = strlen(cInput);
	for (i=0; i < iNum; i++)
	{
		if (cGet == cInput[i])
		{
			iIndex = i;
			iIndex++;
		    break;
		}
	}

	return iIndex;
}

void menu(void)
{
	printf("1.  Enter a string of characters\n");
	printf("2.  Display the current string\n");
	printf("3.  Write current string to file\n");
	printf("4.  Read a string from a file\n");
	printf("5.  Search for a character\n");
	printf("6.  Count occurences of a specific character\n");
	printf("7.  Replace all occurences\n");
	printf("8.  Produce a summary report on the current string\n");
	printf("9.  Exit\n\n");

}

int modify ( const char x, const char y, char *s)
{
	int iNum, j, i=0;

	iNum = strlen(s);
	for ( j=0; j < iNum; j++, s= s+1)
	{
		if (x == *s)
		{
			*s = y;
			i++;
		}
	}

	return i;
}

void write_string(File *fp, char *s)
{
	File *ptr;
	int i;

	ptr == fopen(fp, "w");
	if (ptr == NULL)
		


}

When you fopen() a file the first argument is the File Name and the second argument is the file mode. For example, lets say we had a file name called "Foo.Bar". We would do the following:

File *fp = fopen("Foo.Bar", "w);
fp->write(....
fp->close();

There's quite a few things wrong in you function.
Compare with this.
File is not the same that FILE.
File *fp is not a string.
ptr == fopen is not the same that ptr = fopen.

void write_string( char *fp, char *s)
{
    FILE *ptr;
    int i;

    ptr = fopen( fp, "w");
    if (ptr == NULL);

}

>My problem is what is fp, its coming from the main but what is it exactly?

I'll tell you what exactly is. It is a function from The Outer Limits. It's so far out there that it doesn't even get call once inside main. And fp is nothing more that another alternative dimension or reality if you will.

Maybe this link can help anyone that searchs for this post.
Click here.

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