Question

I don’t understand what the %s and d% do in this C code:

for (i=0;i<sizeof(code)/sizeof(char*); i++) {
    printf("%s%d%s%d\n", "Length of String ", i, " is ", strlen(code[i]));
    str = code[i];
    printf("%s%d%s%c\n","The first character in string ", i, " is ", str[0]);
}

I’m new to the C language and my background is in Java.

• What do the %s%d%s%d symbols denote?
• Why are there so many of them?
• Is the comma used here for concatenation instead of a +?

Answer 1

The printf() family of functions uses % character as a placeholder. When a % is encountered, printf reads the characters following the % to determine what to do:

%s - Take the next argument and print it as a string
%d - Take the next argument and print it as an int

See this Wikipedia article for a nice picture: printf format string

The \n at the end of the string is for a newline/carriage-return character.