Write program to convert a string in lower case without using library function?

Answer 1

It is not certain if the question asked to convert lower case to upper case, or upper case to lower case. This answer assumes the latter. You could easily change this around for the former.

ConvertToLower (char*psz) {

while (*psz != '\0') {

switch (*psz) {

case 'A': *psz = 'a'; break;

case 'B': *psz = 'b'; break;

case 'C': *psz = 'c'; break;

case 'D': *psz = 'd'; break;

case 'E': *psz = 'e'; break;

case 'F': *psz = 'f'; break;

case 'G': *psz = 'g'; break;

case 'H': *psz = 'h'; break;

case 'I': *psz = 'i'; break;

case 'J': *psz = 'j'; break;

case 'K': *psz = 'k'; break;

case 'L': *psz = 'l'; break;

case 'M': *psz = 'm'; break;

case 'N': *psz = 'n'; break;

case 'O': *psz = 'o'; break;

case 'P': *psz = 'p'; break;

case 'Q': *psz = 'q'; break;

case 'R': *psz = 'r'; break;

case 'S': *psz = 's'; break;

case 'T': *psz = 't'; break;

case 'U': *psz = 'u'; break;

case 'V': *psz = 'v'; break;

case 'W': *psz = 'w'; break;

case 'X': *psz = 'x'; break;

case 'Y': *psz = 'y'; break;

case 'Z': *psz = 'z'; break;

}

psz++;

}

Warning. Do not be tempted to replace the switch statement with ...

if (*psz >= 'A' && *psz <= 'Z') *psz += 32;

... because that will only work on ASCII implementations, and it is most definitely not portable, such as in EBCDIC implementations.