Manipulação

int main()
{
    double d;

    d = atof( "99.0" );
    printf( "%s%.3f\n%s%.3f\n",
        "O string \"99.0\" convertido em double is ", d,
        "O valor convertido dividido por 2 eh ", d / 2.0 );


    return 0;
}

/*************************************************************************************************/

int main()
{
    char sentenca[ 80 ];
    void reverse( const char * const );

    printf( "Entre com uma linha de texto:\n" );
    gets( sentenca );

    printf( "\nA linha impressa na ordem inversa eh:\n" );
    reverse( sentenca );

    return 0;
}

void reverse( const char * const sPtr )
{
    if ( sPtr[ 0 ] == '\0' )
        return;
    else {
        reverse( &sPtr[ 1 ] );
        putchar( sPtr[ 0 ] );
    }
}

/*************************************************************************************************/

int main()
{
    char s1[ 20 ] = "Feliz ";
    char s2[] = "Ano Novo ";
    char s3[ 40 ] = "";

    printf( "s1 = %s\ns2 = %s\n", s1, s2 );
    printf( "strcat( s1, s2 ) = %s\n", strcat( s1, s2 ) );
    printf( "strncat( s3, s1, 6 ) = %s\n", strncat( s3, s1, 6 ) );
    printf( "strcat( s3, s1 ) = %s\n", strcat( s3, s1 ) );
return 0;

}

/*************************************************************************************************/

#include <string.h>

int main()
{
    const char *string1 = "O valor é 3.14159";
    const char *string2 = "aeoi lsOrv";

    printf ( "%s%s\n%s%s\n\n%s\n%s%u\n",
    "string1 = ", string1, "string2 = ", string2,
    "O tamanho do segmento inicial de string1",
    "contendo so caracteres do string2 = ",
    strspn( string1, string2 ) );

return 0;
}

/*************************************************************************************************/

int main()
{
    char string[] = "Esta é uma frase com 7 tokens";
    char *tokenPtr;

    printf("%s\n%s\n\n%s\n",
        "O string a ser dividido é:", string,
        "Os tokens são:" );

    tokenPtr = strtok( string, " " );

    while ( tokenPtr != NULL ) {
        printf( "%s\n", tokenPtr );
        tokenPtr = strtok( NULL, " " );
    }

return 0;
}

/*************************************************************************************************/