C Program to Replace Lowercase Characters by Uppercase & Vice-Versa

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This is a C program to replace lowercase characters by uppercase & vice-versa.

Problem Description

This program accepts the sentence and replaces lowercase characters by uppercase & vice-versa.

Problem Solution

1. Take the sentence as input.
2. Using (islower()? toupper():tolower()) function replace lowercase characters by uppercase & vice-versa.
3. Print the output and exit.

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Program/Source Code

Here is source code of the C program to replace lowercase characters by uppercase & vice-versa. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

  1. /*
  2.  * C program to read an English sentence and replace
  3.  * lowercase characters by uppercase and vice-versa.
  4.  * Output the given sentence as well as the converted
  5.  * sentence on two different lines.
  6.  */
  7. #include <stdio.h>
  8. #include <ctype.h>
  9.  
  10. void main()
  11. {
  12.     char sentence[100];
  13.     int count, ch, i;
  14.  
  15.     printf("Enter a sentence \n");
  16.     for (i = 0;(sentence[i] = getchar()) != '\n'; i++)
  17.     {
  18.         ;
  19.     }
  20.     sentence[i] = '\0';
  21.     /*  shows the number of chars accepted in a sentence */
  22.     count = i;
  23.     printf("The given sentence is   : %s", sentence);
  24.     printf("\n Case changed sentence is: ");
  25.     for (i = 0; i < count; i++)
  26.     {
  27.         ch = islower(sentence[i])? toupper(sentence[i]) :
  28. tolower(sentence[i]);
  29.         putchar(ch);
  30.     }
  31. }
Program Explanation

1. Take an an English sentence as input and store it in the array sentence[].
2. Copy the last letter’s position in the array to the variable count.
3. Using for loop and (islower()? toupper():tolower()) function replace lowercase characters by uppercase & vice-versa. Store this in the variable ch.
4. Print the variable ch as output and exit.

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Runtime Test Cases
Enter a sentence
wELCOME tO sANFOUNDRY
The given sentence is   : wELCOME tO sANFOUNDRY
Case changed sentence is: Welcome To Sanfoundry

Sanfoundry Global Education & Learning Series – 1000 C Programs.

Here’s the list of Best Reference Books in C Programming, Data-Structures and Algorithms

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If you wish to look at other example programs on Strings, go to C Programming Examples on Strings. If you wish to look at programming examples on all topics, go to C Programming Examples.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn