C program to convert upper case to lower and vice versa by using string concepts

Converting upper to lower and lower to upper is generally termed as toggle.

Toggle each character means, in a given string, the lower letter is print in upper form and upper case is print in lower letter respectively.

Program

The C program to convert upper case to lower and lower case to upper is given below −

 Live Demo

#include <stdio.h>
#define MAX 100
void toggle(char * string);
int main(){
   char string[MAX];
   printf("enter the string need to be toggle :
");
   gets(string);
   toggle(string);
   printf("final string after toggling is:
");
   printf("%s
", string);
   return 0;
}
void toggle(char * string){
   int i=0;
   while(string[i]!='\0'){
      if(string[i] >= 'a' && string[i] <= 'z'){
         string[i] = string[i] - 32;
      }
      else if(string[i] >= 'A' && string[i] <= 'Z'){
         string[i]= string[i] + 32;
      }
      i++;
   }
}

Output

When you run the above mentioned program, you will get the following output −

enter the string need to be toggle :
TutoRialS PoinT C ProgrAmmIng LanGuage
final string after toggling is:
tUTOrIALs pOINt c pROGRaMMiNG lANgUAGE

Program

The C program to convert upper to lower and lower to upper by using the pre-defined function is as follows −

 Live Demo

#include <stdio.h>
int main(){
   int i, length = 0;
   char string[] = "TutORial";
   length = sizeof(string)/sizeof(string[0]);
   for(i = 0; i < length; i++){
      if(isupper(string[i])){
         string[i] = tolower(string[i]);
      }
      else if(islower(string[i])){
         string[i] = toupper(string[i]);
      }
   }
   printf("final string after conversion: %s", string);
   return 0;
}

Output

The output is as follows −

final string after conversion : tUTorIAL