Problem occur in case structure

I am doing my project to implement a typing tutor application in turbo C compiler (this is the limit), this function is actually a look up table for x,y and key character but it is returning a garbage value at first value of that I passed in argument. From second onwards it starts doing right. Note that that x,y are pointers to return two values at time. Please CHECK what is my mistake.

s1 = "ASDF JKL; ADSF JLK; ";
char take_xy(char s1[], int j, int *x, int *y)
{
    char ch;
    switch(s1[j])
    {
        case 'Q' :  *x = 137;   *y = 244;   ch = 'Q';   break;
        case 'W' :  *x = 160;   *y = 244;   ch = 'W';   break;
        case 'E' :  *x = 183;   *y = 244;   ch = 'E';   break;
        case 'R' :  *x = 206;   *y = 244;   ch = 'R';   break;
        case 'T' :  *x = 229;   *y = 244;   ch = 'T';   break;
        case 'Y' :  *x = 252;   *y = 244;   ch = 'Y';   break;  
        case 'U' :  *x = 275;   *y = 244;   ch = 'U';   break;
        case 'I'  : *x = 298;   *y = 244;   ch = 'I';   break;
        case 'O' :  *x = 321;   *y = 244;   ch = 'O';   break;
        case 'P' :  *x = 344;   *y = 244;   ch = '开发者_开发知识库P';   break;

        case 'A' :  *x = 144;   *y = 268;   ch = 'A';   break;
        case 'S' :  *x = 167;   *y = 268;   ch = 'S';   break;
        case 'D' :  *x = 190;   *y = 268;   ch = 'D';   break;
        case 'F' :  *x = 213;   *y = 268;   ch = 'F';   break;
        case 'G' :  *x = 236;   *y = 268;   ch = 'G';   break;
        case 'H' :  *x = 259;   *y = 268;   ch = 'H';   break;
        case 'J' :  *x = 282;   *y = 268;   ch = 'J';   break;
        case 'K' :  *x = 305;   *y = 268;   ch = 'K';   break;
        case 'L' :  *x = 328;   *y = 268;   ch = 'L';   break;
        case ';' :  *x = 351;   *y = 268;   ch = ';';   break;
//      case ''' :  *x = 374;   *y = 268;   ch = ''';   break;

        case 'Z' :  *x = 162;   *y = 292;   ch = 'Z';   break;
        case 'X' :  *x = 185;   *y = 292;   ch = 'X';   break;
        case 'C' :  *x = 208;   *y = 292;   ch = 'C';   break;
        case 'V' :  *x = 231;   *y = 292;   ch = 'V';   break;
        case 'B' :  *x = 254;   *y = 292;   ch = 'B';   break;
        case 'N' :  *x = 277;   *y = 292;   ch = 'N';   break;
        case 'M' :  *x = 300;   *y = 292;   ch = 'M';   break;
        case '?' :  *x = 369;   *y = 292;   ch = '?';   break;

        case ' ' :  *x = 189;   *y = 316;   ch = ' ';   break;

    }
    return ch;
}    

I would check how you are calling this function. I would guess that the 'j' parameter is less than 0 or greater than 19.

Also run in a debugger and check the value of all your parameters the first time it is called.

As @Matthew Flaschen indicated, let's see the calling code.

EDIT

You might want to also add a default clause to catch anything that doesn't match.

It looks like the contents of sl[j] may not covered in that switch, so "ch" has whatever default value it contains when created on the stack.

I would do one of the following:

1. Normalize the contents of sl[j] before using it in the switch.
2. Add a "default" tag to the switch.
3. Initialize "ch" to some default value when you declare it (equivalent to option 2).

There is nothing wrong with the code you have posted, the error must be somewhere else.