strcat(),strcmp(),strrev() User Defined Functions in C

Problem:

Write a C program to implement user defined strcmp(), strcpy(), strrev(), strcat(), strupr(), strlwr() functions in C. Also write main() function to illustrate the use of all user defined functions.

C Program / Source Code:

Here is the source code for strcat() user defined function in C.

/* Aim: For the following standard functions write corresponding user defined functions and write a menu driven program to use them.
1]strcat() 2]strcmp() 3]strrev() 4]strupr() 5]strlwr() 6]strcpy()
*/

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

void StrCat(char str[],char str1[]); // StrCat() user defined Function in c Prototype
void StrCmp(char str[],char str1[]); // StrCmp() Function Prototype
void StrRev(char str[]); // StrRev() Function Prototype
void StrUpr(char str[]); // StrUpr() Function Prototype
void StrLwr(char str[]); // StrLwr() Function Prototype
void StrCpy(char str[],char str1[]); // StrCpy() Function Prototype
 
int main()
{
 char str[20],str1[20],ch;
 int ope;

 do{
 printf("\n****Menu****");
 printf("\n 1.strcat");
 printf("\n 2.strcmp");
 printf("\n 3.strrev");
 printf("\n 4.strupr");
 printf("\n 5.strlwr");
 printf("\n 6.strcpy");
 printf("\n 7.Exit \n");

 printf("\n Which function do you want to use:- ");
 scanf("%d",&ope);

 if(ope==1 || ope==2)
 { 
 printf("\n Enter first string (20 Characters Max):- ");
 scanf("%s",str);
 printf("\n Enter second string (20 Characters Max):- ");
 scanf("%s",str1);
 } 
 else if(ope==3 || ope==4 || ope==5 || ope==6)
 {
 printf("\n Enter any string (20 Characters Max):- ");
 scanf("%s",str);
 }

 switch(ope)
 {
 case 1:
 StrCat(str,str1);
 break;

 case 2:
 StrCmp(str,str1);
 break;

 case 3:
 StrRev(str);
 break;

 case 4:
 StrUpr(str);
 break;

 case 5:
 StrLwr(str); 
 break;

 case 6:
 StrCpy(str1,str); // contents of string are copied into string1 
 break;
  
 default:
 printf("\n Invalid Choice. \n \n");
 }}while(ch!=7);

 return 0;

} // End of main

// StrCat() user defined function in C to concatenate two strings without using string functions
void StrCat(char str[],char str1[])
{
 int i,j=0;

 for(i=(strlen(str)-1);i<=(strlen(str)+strlen(str1)-2);i++)
 { 
 str[i]=str1[j];
 j++;
 }
 
 printf("\n The Concatenation of two strings is \"%s\" \n \n",str);

}

// StrCmp() function to compare two strings without string library
void StrCmp(char str[],char str1[])
{
 int i,j=0,LED=0;

 for(i=0;i<=strlen(str)-1;i++)
 { 
 if(str[i]!=str1[j])
 {
  LED=1;
  break;
 }
 j++;
 }

 if(LED==0)
  printf("\n Two strings is \"%s\" and \"%s\" are same \n \n",str,str1);   
 else
  printf("\n Two strings is \"%s\" and \"%s\" are  not same \n \n",str,str1); 
}

// Implicit declaration of StrRev() function to reverse a string without using string functions
void StrRev(char str[])
{
 char str1[20];
 int i,j=0;

 for(i=strlen(str)-1;i>=0;i--)
 {
 str1[j]=str[i];
 j++;
 }

 printf("\n The reverse string of \"%s\" is \"%s\" \n \n",str,str1);
}

// StrUpr() Function to make all characters in upper case in given string
void StrUpr(char str[])
{
 char ch,str1[20];
 int i;

 for(i=0;i<=strlen(str)-1;i++)
 {
 ch=toupper(str[i]);
 str1[i]=ch;
 }
 
 printf("\n The uppercase string of \"%s\" is \"%s\" \n \n",str,str1);

}

// StrLwr() Function to make characters lower case in given string
void StrLwr(char str[])
{
 char ch,str1[20];
 int i;

 for(i=0;i<=strlen(str)-1;i++)
 {
 ch=tolower(str[i]);
 str1[i]=ch;
 }
 
 printf("\n The lowercase string of \"%s\" is \"%s\" \n \n",str,str1);
}


// StrCpy function to make to copy a string without using standard library function
void StrCpy(char str[],char str1[])
{
 int i,j=0;
 for(i=0;str1[i]!='\0';i++)
 {
 *(str+j)=str1[i];
 j++;
 }

 *(str+j)='\0';

printf("\n Str1 is copied into Str \n");  
printf("\n Str= %s \n",str);

}

/* Output of above code / Runtime case:-

 ****Menu****
 1.strcat
 2.strcmp
 3.strrev 
 4.strupr
 5.strlwr
 6.strcpy
 7.Exit 

 Which function do you want to use:- 3

 Enter any string (20 Characters Max):-Helloo

 The reverse string of "Helloo" is "oolleH" 

*/

If you are using inbuilt strrev() function you may receive Implicit Declaration of strrev function error. Follow the link to get the solution.