C Program to convert a string from Uppercase to Lowercase

In this C Programming example, we will implement the program to convert a string from upper case to lower case and print the output on the screen.

1. String Conversion – Upper Case to Lower Case

String Case Conversion is a process to convert each character of a string to either Uppercase or to Lowercase characters. In this example, we will convert from uppercase string to lowercase using their ASCII values.

Example: 
Enter the string which needs to be converted : HAPPY BIRTHDAY
The String in Upper Case is = happy birthday

Helpful topics to understand this program better are-

• Data Types in C
• Console Input / Output in C
• Functions in C
• For and while loop in C

2. C Program to convert a string from upper case to lower case

Let’s discuss the execution(kind of pseudocode) for the program to convert a string from upper case to lower case in C.

1. Initially, the program will prompt the user to enter the string that needs to be converted.
2. The string is now passed to a function void convertUpperToLower().
3. In the void convertUpperToLower() function, For loop is used to convert the entered string into a lower case string.
4. If the string is in the upper case then convert the string into the lower case by adding 32 from their ASCII value.
5. Finally, output the string on the console.

Let us now implement the above execution of the program to convert string from upper case to lower case.

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

char string[1000];

void convertUpperCaseToLower() {
  int i;
  for (i = 0; string[i] != '\0'; i++) {
    if (string[i] >= 'A' && string[i] <= 'Z') {
      string[i] = string[i] + 32;
    }
  }
}
int main() {
  printf("\nEnter the string : ");
  gets(string);
  convertUpperCaseToLower();
  printf("\nThe String in Lower Case = %s", string);
  return 0;
}

Note: The above program can also be implemented using a while loop as well.

Output
Enter the string : UPPER TO LOWER
String in Lower Case = upper to lower

3. Conclusion

In this C Programming example, we have discussed how to convert a string from upper case to lower case using the ASCII values.

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